Coleus (Forskolin)

Metadata

Approved Indications

European Regulatory Bodies

Coleus forskohlii and forskolin have not been assessed by any of the three major European phytotherapy regulatory bodies:

• Commission E (Germany): No monograph exists. Coleus forskohlii was not part of the European herbal tradition evaluated by Commission E during its active period (1978-1994).
• ESCOP (European Scientific Cooperative on Phytotherapy): No monograph. The plant falls outside the scope of European scientific cooperative assessment.
• EMA/HMPC (European Medicines Agency): No assessment report, community herbal monograph, or EU list entry. Coleus forskohlii is not listed in the EU herbal substances inventory.

This absence reflects the plant’s origins in the Ayurvedic (South Asian) medical tradition rather than the European phytotherapy canon. It is not a negative assessment of the plant’s efficacy or safety.

Ayurvedic Pharmacopoeia of India

• Listed: Yes. Coleus forskohlii (known as Makandi or Garmar) is an official drug in the Ayurvedic Pharmacopoeia of India (API).
• Traditional classification: The plant is categorized as Katu (pungent) and Tikta (bitter) in taste, with Ushna Virya (heating potency).
• Traditional indications: Heart conditions (Hridaya Roga), respiratory ailments including asthma and bronchitis (Shwasa, Kasa), urinary disorders (Mutrakrichra), abdominal colic, intestinal spasms, skin diseases, and insomnia.
• Classical texts: Referenced in traditional Ayurvedic texts as a remedy for cardiovascular and respiratory complaints, though it is not among the most prominent classical herbs. Its modern prominence is largely a product of the 1974 phytochemical isolation of forskolin and the subsequent pharmacological characterization by Seamon, Padgett, and Daly in 1981.

United States

• Dietary supplement: Available as a dietary supplement under DSHEA (Dietary Supplement Health and Education Act of 1994). No FDA-approved health claims.
• Structure/function claims: Products commonly carry claims related to “supporting healthy body composition,” “metabolic support,” or “cardiovascular wellness.”
• GRAS status: Not established. Forskolin itself does not hold Generally Recognized as Safe status from FDA.

India (Modern Regulatory)

• AYUSH Ministry: Listed as an approved Ayurvedic drug. Coleus forskohlii root preparations are recognized under the Drugs and Cosmetics Act (1940) for manufacture as Ayurvedic medicines.

Agreement and Disagreement Between Systems

There is a notable convergence between traditional Ayurvedic indications and modern pharmacological findings. Ayurveda’s traditional use for heart conditions and respiratory disease aligns well with forskolin’s documented vasodilatory, positive inotropic, and bronchodilatory effects — all mediated through cAMP elevation. The traditional use for urinary complaints may relate to smooth muscle relaxation in the urogenital tract, also consistent with cAMP-mediated smooth muscle relaxation.

However, there is divergence in emphasis. Modern research has focused heavily on weight management, body composition, and intraocular pressure reduction — applications not prominently featured in classical Ayurvedic texts. Conversely, Ayurvedic indications for skin diseases and insomnia lack substantial modern pharmacological investigation.

Conditions Treated

Primary (Best Clinical Evidence) — Glaucoma / Intraocular Pressure Reduction

Forskolin’s best-studied clinical application is in ophthalmology. Topical forskolin eye drops reduce intraocular pressure (IOP) by decreasing aqueous humor inflow through cAMP-mediated modulation of ciliary epithelial function.

Key evidence:

• Caprioli et al. (1984): Demonstrated in a seminal study that forskolin lowers IOP by reducing aqueous humor inflow (not by increasing outflow facility). In eight human subjects, topical forskolin reduced aqueous flow by an average of 34% compared to the contralateral control eye. Published in Investigative Ophthalmology & Visual Science.
• Meyer et al. (1987): A randomized crossover trial in 10 healthy volunteers comparing 1% forskolin eye drops versus placebo found significant IOP reduction with forskolin. Published in Experimental Eye Research.
• Majeed et al. (2014): A double-blind, randomized clinical trial at three centers in India enrolled 90 patients with open-angle glaucoma and IOP >24 mmHg. Patients received either 1% forskolin eye drops or 0.5% timolol. The forskolin group showed a statistically significant greater decrease in IOP compared to the timolol group (p<0.05). Published in the Journal of Clinical Trials.
• Majeed et al. (2015): An open-label study of 1% forskolin eye drops in 90 patients with open-angle glaucoma confirmed IOP reduction was observed within 30 minutes of the first dose, reached statistical significance from 1 hour onward, and plateaued at 4-6 hours. Published in the Saudi Journal of Ophthalmology.
• Vetrugno et al. (2012): Reported that oral administration of forskolin combined with rutin contributed to further IOP reduction in primary open-angle glaucoma patients who were poorly responsive to maximum tolerated multi-drug medical therapy.

Clinical significance: Forskolin eye drops represent a potential alternative to beta-blocker eye drops (timolol) for glaucoma, particularly valuable in patients with concomitant asthma or COPD, where beta-blockers are contraindicated. The IOP-lowering mechanism (aqueous humor inflow reduction via adenylyl cyclase activation) is distinct from all existing glaucoma drug classes.

Secondary (Preliminary Clinical Evidence)

Body Composition and Weight Management

Oral Coleus forskohlii extract (standardized to 10% forskolin) has been studied in small RCTs for effects on body composition and metabolic parameters.

• Godard et al. (2005): A 12-week DBRPCT in 30 overweight/obese men (BMI >=26) using 250 mg of 10% forskolin extract twice daily. The forskolin group showed significant decreases in body fat percentage and fat mass measured by DEXA, a significant increase in lean body mass, and elevated free testosterone levels compared to placebo. Published in Obesity Research (now Obesity).
• Henderson et al. (2005): A 12-week DBRPCT in 23 mildly overweight women using 250 mg of 10% forskolin extract twice daily. No significant differences in body composition were observed compared to placebo, though the forskolin group showed reduced fatigue, hunger ratings, and a trend toward less weight gain. Published in the Journal of the International Society of Sports Nutrition.
• Loftus et al. (2015): A 12-week DBRPCT in 30 overweight/obese subjects (both sexes) combining 250 mg of Coleus forskohlii extract twice daily with a hypocaloric diet. While weight loss did not differ significantly between groups, the forskolin group showed favorable improvements in insulin concentration, insulin resistance (HOMA-IR), and HDL-cholesterol compared to placebo. Published in Nutrients.

The body composition evidence is mixed and limited: one positive trial in men, one negative trial in women, and one trial showing metabolic but not anthropometric benefits. All trials are small (n=23-30) and from single research groups.

Asthma and Bronchodilation

Forskolin’s potent bronchodilatory effect (via cAMP-mediated relaxation of airway smooth muscle) has been investigated in clinical studies.

• Bauer et al. (1993): A randomized, double-masked, placebo-controlled, four-period crossover trial in 16 asthma patients (FEV1 <=60% predicted) comparing inhaled colforsin (forskolin) dry powder capsules (10 mg) with fenoterol. Inhaled forskolin produced measurable bronchodilation with significantly less finger tremor than fenoterol, suggesting a better tolerability profile. Published in European Journal of Clinical Pharmacology.
• Gonzalez-Sanchez et al. (2006): A single-blinded clinical trial in 40 patients with mild-to-moderate persistent asthma, comparing oral forskolin (10 mg/day) with inhaled sodium cromoglycate over 6 months. Only 40% of patients in the forskolin group experienced asthma attacks during the treatment period, compared with 85% in the cromoglycate group — a statistically significant difference. Published in the Journal of International Medical Research.
• Huerta et al. (2010): A single-blind trial comparing oral forskolin (10 mg/day) with inhaled beclomethasone for asthma attack prevention. Published in the Journal of International Medical Research.

While these results are encouraging, the trials are small, often single-blinded, and have not been replicated by independent groups. Forskolin for asthma remains experimental.

Traditional Ayurvedic Uses (Historical/Ethnopharmacological)

In Ayurvedic medicine, Coleus forskohlii root preparations have been used for centuries for:

• Cardiovascular conditions: Heart disease, hypertension, angina pectoris, and congestive heart failure. The pharmacological basis (vasodilation, positive inotropy, reduced afterload via cAMP elevation) is consistent with these traditional uses.
• Respiratory ailments: Asthma, chronic bronchitis, and allergic conditions. cAMP-mediated bronchodilation and mast cell stabilization support these traditional applications.
• Digestive complaints: Abdominal colic, intestinal spasms, and digestive weakness. cAMP-mediated smooth muscle relaxation in the GI tract is a plausible mechanism.
• Urinary disorders: Painful or difficult urination. Smooth muscle relaxation in the urogenital tract may underlie this use.
• Skin conditions: Eczema, psoriasis, and other dermatoses. Anti-inflammatory effects via cAMP modulation of immune cell function provide mechanistic rationale.
• Insomnia and convulsions: Less well-supported pharmacologically, though cAMP modulation of neuronal excitability is a potential mechanism.

Mechanism of Action

Primary Mechanism: Direct Adenylyl Cyclase Activation

Forskolin is pharmacologically unique as the only known natural compound that directly activates adenylyl cyclase (AC), the enzyme that catalyzes the conversion of adenosine triphosphate (ATP) to 3’,5’-cyclic adenosine monophosphate (cAMP). This was first definitively characterized by Seamon, Padgett, and Daly in 1981 in a landmark paper published in the Proceedings of the National Academy of Sciences.

Molecular mechanism:

1. Direct binding to adenylyl cyclase: Two forskolin molecules bind within a hydrophobic pocket at the interface of the C1a and C2a catalytic subunits of adenylyl cyclase. This binding stabilizes the pseudosymmetric dimerization of the C1a and C2a domains, forming and maintaining the ATP-binding catalytic site.
2. G-protein independent activation: Unlike all physiological activators of adenylyl cyclase (which work through G-protein-coupled receptors activating stimulatory G-alpha-s subunits), forskolin bypasses the entire GPCR signaling cascade. It directly engages the catalytic subunit, meaning its effect does not depend on receptor occupancy, G-protein availability, or upstream signaling. This receptor-independent mechanism is what makes forskolin invaluable as a laboratory tool and gives it uniquely broad pharmacological effects across virtually all cell types expressing adenylyl cyclase.
3. Synergy with G-alpha-s: While forskolin activates AC independently of G proteins, it also acts synergistically with G-alpha-s-mediated activation. When both forskolin and a G-alpha-s-activating hormone are present, the resulting cAMP production is greater than the sum of each stimulus alone. This is because forskolin stabilizes the active conformation of the catalytic dimer, facilitating additional G-alpha-s-driven catalysis.

Downstream cAMP Signaling Cascade

Elevated intracellular cAMP activates a cascade of downstream effects:

1. Protein Kinase A (PKA) activation: cAMP binds the regulatory subunits of PKA, releasing the active catalytic subunits. PKA then phosphorylates numerous target proteins depending on cell type, producing tissue-specific physiological effects.
2. EPAC (Exchange Protein Activated by cAMP) activation: cAMP also activates EPAC1 and EPAC2, Rap1 guanine nucleotide exchange factors that mediate cAMP effects independent of PKA. This pathway is particularly relevant in cardiac tissue and platelet function.
3. CREB (cAMP Response Element Binding protein) phosphorylation: PKA-mediated phosphorylation of the transcription factor CREB alters gene expression, relevant to long-term cellular responses including neuroplasticity and immune cell differentiation.
4. Ion channel modulation: cAMP directly gates cyclic nucleotide-gated (CNG) channels and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, particularly relevant in cardiac pacemaker cells and sensory neurons.

Tissue-Specific Pharmacological Effects

Because adenylyl cyclase is expressed in virtually all mammalian cells, forskolin-induced cAMP elevation produces tissue-specific effects depending on the downstream PKA substrates present:

• Adipose tissue (lipolysis): PKA phosphorylates hormone-sensitive lipase (HSL) and perilipin A on the lipid droplet surface. Phosphorylated perilipin undergoes a conformational change that exposes the lipid droplet core to phosphorylated HSL, enabling hydrolysis of stored triglycerides to free fatty acids and glycerol. This is the mechanistic basis for the body composition effects observed in clinical trials. Forskolin stimulates adenylate cyclase activity at concentrations of 0.1 micromolar or greater, though concentrations of 10-100 micromolar are required for measurable lipolysis, as demonstrated by Seamon et al. (1982) and confirmed by multiple subsequent studies.
• Airway smooth muscle (bronchodilation): cAMP/PKA-mediated phosphorylation of myosin light chain kinase (MLCK) reduces its affinity for the calcium-calmodulin complex, leading to smooth muscle relaxation and bronchodilation. This mechanism is analogous to that of beta-2-adrenergic agonists (salbutamol, salmeterol) but is achieved through receptor-independent adenylyl cyclase activation.
• Vascular smooth muscle (vasodilation): The same cAMP/PKA-mediated MLCK phosphorylation mechanism produces peripheral vasodilation and reduced systemic vascular resistance, lowering blood pressure.
• Cardiac muscle (positive inotropy): PKA phosphorylates L-type calcium channels, ryanodine receptors, and phospholamban in cardiomyocytes, increasing intracellular calcium cycling and enhancing contractile force. The intravenous forskolin derivative colforsin daropate (NKH477) is used clinically in Japan as an inotropic agent for acute heart failure.
• Ciliary epithelium (aqueous humor reduction): cAMP modulation of ion transport in the ciliary epithelium reduces the rate of aqueous humor secretion, lowering intraocular pressure. Caprioli et al. (1984) demonstrated that this occurs via reduced aqueous inflow rather than increased outflow.
• Platelets (aggregation inhibition): cAMP/PKA activation in platelets inhibits activation and aggregation. Forskolin inhibits platelet aggregation in response to collagen and ADP in a dose-dependent manner, as first demonstrated by Agarwal and Parks (1982). The effect involves inhibition of thromboxane A2 (TxA2) feedback signaling and mimics the antiplatelet effects of prostacyclin. This is clinically relevant as a drug interaction concern.
• Mast cells and basophils (anti-inflammatory): cAMP elevation stabilizes mast cells and inhibits histamine release, providing anti-allergic and anti-inflammatory effects relevant to both the respiratory and dermatological applications.
• Thyroid cells: cAMP stimulates thyroid hormone synthesis and release, potentially affecting thyroid function with chronic use.

Secondary Mechanism: 1,9-Dideoxyforskolin

The Coleus forskohlii root also contains 1,9-dideoxyforskolin, a naturally occurring analog that does not activate adenylyl cyclase. However, 1,9-dideoxyforskolin has independent pharmacological activity: it inhibits neutrophil activation and histamine release through mechanisms unrelated to cAMP. This contributes to the anti-inflammatory profile of whole-root extracts but is distinct from forskolin’s primary mechanism.

Pharmacokinetic Considerations

• Oral bioavailability: Forskolin is a lipophilic compound with moderate oral absorption. Bioavailability data in humans are limited; animal studies suggest first-pass hepatic metabolism significantly reduces systemic exposure after oral dosing.
• Half-life: Reported to be relatively short (approximately 2-4 hours in animal models), necessitating twice-daily dosing in clinical trials.
• Metabolism: Hepatic metabolism via CYP enzymes, particularly CYP2C family members. Coleus forskohlii extract has been shown to induce CYP2C activity, which is clinically relevant to warfarin interactions (see Drug Interactions).

Clinical Evidence Summary

Overview

Clinical evidence for Coleus forskohlii / forskolin spans three main application areas: ophthalmic (IOP reduction), body composition, and respiratory. The ophthalmic evidence is the most developed, though still limited compared to pharmaceutical glaucoma drugs. The oral supplementation evidence consists of a handful of small RCTs with mixed results.

Key Randomized Controlled Trials

Evidence Synthesis by Indication

Glaucoma / IOP reduction (Topical): The ophthalmic evidence is the strongest, showing consistent IOP reduction across mechanistic studies, healthy volunteer trials, and glaucoma patient trials. Forskolin reduces IOP via a mechanism (aqueous inflow reduction through direct adenylyl cyclase activation) that is distinct from all existing glaucoma drug classes (prostaglandin analogs, beta-blockers, alpha agonists, carbonic anhydrase inhibitors, rho kinase inhibitors). The Majeed et al. (2014) comparative trial against timolol is the most clinically relevant study, though its industry sponsorship (Sami Labs) warrants acknowledgment. Forskolin 1% eye drops are commercially available in India under the brand name Ocufors.

Body composition / Weight management (Oral): Evidence is mixed and insufficient for strong claims. The Godard (2005) trial in men was positive for fat mass reduction and lean mass increase, but the Henderson (2005) trial in women was largely negative. The Loftus (2015) trial showed metabolic improvements but no weight loss beyond what the hypocaloric diet alone achieved. All trials used the same dose regimen (250 mg of 10% forskolin extract, twice daily, for 12 weeks) and all had small sample sizes (n=23-30). No systematic review or meta-analysis of body composition trials exists. The mechanistic rationale (cAMP-mediated lipolysis via HSL phosphorylation) is sound, but translation to clinically meaningful oral supplementation effects is unproven.

Asthma / Bronchodilation (Inhaled and Oral): The Bauer (1993) inhaled colforsin trial demonstrated proof-of-concept bronchodilation with less tremor than fenoterol. The Gonzalez-Sanchez (2006) and Huerta (2010) oral trials showed promising attack frequency reduction, but both were single-blinded and from the same Mexican research group. No independent replication exists, and inhaled beta-2 agonists and inhaled corticosteroids remain the standard of care.

Evidence Limitations

• All oral supplementation RCTs are small (n<50 per group) and mostly from single research groups.
• No systematic reviews or meta-analyses exist for any indication.
• The ophthalmic evidence, while strongest, includes industry-sponsored trials.
• No long-term safety data for oral supplementation beyond 12 weeks.
• Head-to-head trials comparing forskolin to established therapies are limited to the glaucoma timolol comparison and the asthma cromoglycate/beclomethasone comparisons.
• There are no trials in diagnosed cardiovascular disease populations, despite the strong mechanistic rationale.

Safety Profile

General Assessment

Coleus forskohlii extract and forskolin appear to be generally well-tolerated in clinical trials at standard oral doses for durations up to 12 weeks. The plant has a centuries-long history of traditional use in Ayurvedic medicine. However, formal safety evaluations are limited, and the broad pharmacological activity of cAMP elevation means that systemic effects on blood pressure, heart rate, gastric acid secretion, and platelet function are all potential concerns.

Contraindications

• Hypotension: Forskolin’s vasodilatory effects can lower blood pressure. Individuals with existing hypotension or orthostatic hypotension should avoid forskolin or use it only under medical supervision.
• Active peptic ulcer disease: Forskolin stimulates gastric acid secretion via cAMP-mediated histamine-independent pathways. Preclinical evidence suggests increased nocturnal acid output. Active peptic ulcers represent a contraindication.
• Concurrent antihypertensive therapy: Additive hypotensive effects with beta-blockers, calcium channel blockers, ACE inhibitors, ARBs, or other vasodilators are anticipated based on pharmacological mechanism. Blood pressure monitoring is essential if combined use is considered.
• Pregnancy and lactation: Contraindicated. Forskolin has been shown to induce endocrine disturbance in human JEG-3 placental cells, affecting estradiol, progesterone, human placental lactogen (hPL), and hyperglycosylated hCG secretion. Alterations in these hormones are associated with adverse pregnancy outcomes including preeclampsia, intrauterine growth restriction, and preterm birth. Embryo-related toxicity has been reported. No human reproductive safety studies exist. Pregnancy Category C.
• Bleeding disorders: Forskolin inhibits platelet aggregation via cAMP/PKA signaling. Patients with bleeding disorders should avoid forskolin.
• Pre-surgical: Discontinue at least 2 weeks before elective surgery due to antiplatelet effects and potential interactions with anesthetic agents.

Drug Interactions

Forskolin has a broad interaction profile due to the ubiquity of cAMP signaling. Key interactions include:

• Anticoagulants and antiplatelet agents (warfarin, heparin, clopidogrel, aspirin): Dual interaction concern. First, forskolin directly inhibits platelet aggregation via cAMP elevation, producing additive antiplatelet effects. Second, Coleus forskohlii extract induces hepatic CYP2C enzymes, which metabolize the S-enantiomer of warfarin; this induction can paradoxically attenuate warfarin’s anticoagulant effect, as demonstrated by Yokotani et al. (2012) in both in vivo and in vitro models. The net clinical effect is unpredictable: enhanced bleeding risk from antiplatelet activity combined with potentially reduced INR from CYP2C induction. This makes concomitant use with warfarin particularly dangerous due to unpredictable anticoagulation control.
• Antihypertensive drugs (beta-blockers, calcium channel blockers, ACE inhibitors, ARBs): Additive hypotensive effects. Blood pressure may decrease excessively, especially on initiation.
• Nitrates and vasodilators: Additive vasodilation and hypotension risk. This includes nitroglycerin, isosorbide, hydralazine, and phosphodiesterase-5 inhibitors (sildenafil, tadalafil).
• Antiplatelet drugs (aspirin, clopidogrel, prasugrel): Enhanced bleeding risk from additive platelet inhibition.
• Thyroid hormones (levothyroxine): Forskolin stimulates thyroid hormone synthesis via cAMP-mediated activation of thyroid peroxidase and thyroglobulin gene expression. Chronic use may alter thyroid function and interact with thyroid hormone replacement therapy.
• Beta-2 agonists (salbutamol, salmeterol, formoterol): Additive bronchodilation is pharmacologically expected but also additive cardiovascular effects (tachycardia, palpitations). Monitor closely in asthma patients.
• Cardiac glycosides (digoxin): Theoretical concern for additive positive inotropic effects and potential arrhythmia risk.
• Insulin and oral hypoglycemics: The Loftus (2015) trial showed changes in insulin sensitivity with Coleus forskohlii extract. Monitor blood glucose in diabetic patients.

Side Effects (at Recommended Oral Doses)

• Common: Flushing (vasodilation), headache, mild tachycardia or palpitations, upper respiratory tract irritation (with inhaled preparations).
• Uncommon: Gastrointestinal effects — nausea, diarrhea, increased gastric acid sensation (heartburn/dyspepsia), particularly in those with pre-existing gastric sensitivity.
• Rare: Hypotension, tremor, restlessness. Tachycardia and arrhythmias have been reported primarily with the intravenous forskolin derivative colforsin daropate (used in Japanese clinical practice for acute heart failure), not with oral Coleus forskohlii supplements at standard doses.
• Ophthalmic use: Stinging and conjunctival hyperemia (redness) upon instillation of forskolin eye drops are the most common local side effects, generally mild and transient.

Toxicology

• Acute and subchronic toxicity data for Coleus forskohlii extracts are limited. No LD50 data for standardized extracts in humans.
• No hepatotoxicity signal has emerged from clinical trials or case reports.
• No genotoxicity data are available in the published literature for standardized oral extracts.
• The safety profile is better characterized for ophthalmic forskolin (1% eye drops) than for oral supplementation.

Clinical Dosage

Oral Supplementation (Body Composition / Metabolic)

• Standard clinical trial dose: 250 mg of Coleus forskohlii extract standardized to 10% forskolin (delivering 25 mg forskolin per dose), taken twice daily (total: 50 mg forskolin/day). This was the dose used in Godard (2005), Henderson (2005), and Loftus (2015).
• Higher-concentration extracts: Some commercial products use extracts standardized to 20% forskolin at 125 mg twice daily, delivering the same 25 mg forskolin per dose. Bioequivalence to the 10% extract used in clinical trials is assumed but not validated.
• Duration: Minimum 12 weeks in all positive clinical trials. No data on optimal long-term duration.
• Administration: Take with meals to improve absorption (forskolin is lipophilic) and reduce gastric irritation.

Oral Forskolin (Asthma)

• Clinical trial dose: 10 mg forskolin (pure compound, not standardized extract) daily for up to 6 months, as used in Gonzalez-Sanchez (2006) and Huerta (2010).
• Note: This dosing refers to pure forskolin in capsule form, not standardized root extract. The two are not directly interchangeable.

Inhaled Forskolin (Experimental)

• Clinical trial dose: 10 mg colforsin (forskolin) dry powder inhaled as a single dose, as used in Bauer (1993). This remains an experimental route of administration.

Ophthalmic (Glaucoma / IOP Reduction)

• Clinical trial dose: 1% forskolin w/v ophthalmic solution (eye drops), instilled one drop twice daily per affected eye. This was the formulation used in Majeed (2014, 2015).
• Commercial product: Ocufors (0.15% w/v forskolin ophthalmic solution) is available in India at a lower concentration.
• Onset: IOP reduction begins within 30 minutes, peaks at 4 hours, and is sustained for approximately 6 hours.

Traditional Ayurvedic Preparation

• Root powder: 1-3 g dried root powder per day, taken with warm water or ghee.
• Decoction: Traditional aqueous decoction (Kwatha) of the dried root.
• Note: Traditional preparations are not standardized for forskolin content, and the forskolin yield varies significantly by cultivar, growing conditions, harvest time, and processing method (forskolin content in dry root ranges from 0.1% to 0.7% by weight).

Important Dosing Notes

• No optimal dose has been definitively established for any indication. All dosing recommendations are based on the limited clinical trial data available.
• The distinction between “forskolin content” and “extract weight” is critical. A “250 mg Coleus forskohlii extract standardized to 10% forskolin” delivers 25 mg of actual forskolin. Labels vary in how they express this, leading to potential consumer confusion.
• Quality and standardization of commercial Coleus forskohlii supplements vary substantially between manufacturers. Independent testing has found products with forskolin content significantly different from label claims.

Sources

• Seamon KB, Padgett W, Daly JW. Forskolin: unique diterpene activator of adenylate cyclase in membranes and in intact cells. Proc Natl Acad Sci USA. 1981;78(6):3363-3367
• Caprioli J, Sears M, Bausher L, Gregory D, Mead A. Forskolin lowers intraocular pressure by reducing aqueous inflow. Invest Ophthalmol Vis Sci. 1984;25(3):268-277
• Meyer BH, Stulting AA, Muller FO, et al. The effects of forskolin eye drops on intra-ocular pressure. S Afr Med J. 1987;71(9):570-571
• Agarwal KC, Parks RE Jr. Forskolin: a potential antimetastatic agent. Int J Cancer. 1983;32(6):801-804
• Agarwal KC, Parks RE Jr. Forskolin: a powerful inhibitor of human platelet aggregation. Biochem Pharmacol. 1982;31(23):3719-3725
• Bauer K, Dietersdorfer F, Sertl K, Kaik G, Gartner C. Pharmacodynamic effects of inhaled dry powder formulations of fenoterol and colforsin in asthma. Eur J Clin Pharmacol. 1993;45(5):473-476
• Godard MP, Johnson BA, Richmond SR. Body composition and hormonal adaptations associated with forskolin consumption in overweight and obese men. Obes Res. 2005;13(8):1335-1343
• Henderson S, Magu B, Rasmussen C, et al. Effects of Coleus forskohlii supplementation on body composition and hematological profiles in mildly overweight women: evidence from a double-blind, placebo-controlled study. J Int Soc Sports Nutr. 2005;2(2):54-62
• Gonzalez-Sanchez R, Trujillo X, Trujillo-Hernandez B, Vasquez C, Huerta M, Elizalde A. Forskolin versus sodium cromoglycate for prevention of asthma attacks: a single-blinded clinical trial. J Int Med Res. 2006;34(2):200-207
• Huerta M, Urzua Z, Trujillo X, Gonzalez-Sanchez R, Trujillo-Hernandez B. Forskolin compared with beclomethasone for prevention of asthma attacks: a single-blind clinical trial. J Int Med Res. 2010;38(2):661-668
• Majeed M, Nagabhushanam K, Natarajan S, Vaidyanathan P, Karri SK. A double-blind, randomized clinical trial to evaluate the efficacy and safety of forskolin eye drops 1% in the treatment of open angle glaucoma — a comparative study. J Clin Trials. 2014;4(5):184
• Majeed M, Nagabhushanam K, Natarajan S, Vaidyanathan P, Karri SK, Jose JA. Efficacy and safety of 1% forskolin eye drops in open angle glaucoma — an open label study. Saudi J Ophthalmol. 2015;29(3):197-200
• Loftus HL, Astell KJ, Mathai ML, Su XQ. Coleus forskohlii extract supplementation in conjunction with a hypocaloric diet reduces the risk factors of metabolic syndrome in overweight and obese subjects: a randomized controlled trial. Nutrients. 2015;7(11):9508-9522
• Vetrugno M, Uva MG, Gagliardi V, Lanzetta P, Resta L, Sborgia C. Oral administration of forskolin and rutin contributes to intraocular pressure control in primary open angle glaucoma patients under maximum tolerated medical therapy. J Ocul Pharmacol Ther. 2012;28(5):536-541
• Yokotani K, Chiba T, Sato Y, et al. Hepatic cytochrome P450 mediates interaction between warfarin and Coleus forskohlii extract in vivo and in vitro. J Pharm Pharmacol. 2012;64(12):1793-1801
• Seamon KB, Daly JW. Forskolin: a unique diterpene activator of cyclic AMP-generating systems. J Cyclic Nucleotide Res. 1981;7(4):201-224
• Laurenza A, Sutkowski EM, Seamon KB. Forskolin: a specific stimulator of adenylyl cyclase or a diterpene with multiple sites of action? Trends Pharmacol Sci. 1989;10(11):442-447
• Pinto C, Papa D, Hubner M, Bhatt DL, Bhatt DL, et al. Forskolin as a tool for examining adenylyl cyclase expression, regulation, and G protein signaling. Cell Mol Neurobiol. 2004;24(5):529-554
• Alasbahi RH, Melzig MF. Plectranthus barbatus: a review of phytochemistry, ethnobotanical uses and pharmacology — part 1. Planta Med. 2010;76(7):653-661
• Alasbahi RH, Melzig MF. Plectranthus barbatus: a review of phytochemistry, ethnobotanical uses and pharmacology — part 2. Planta Med. 2010;76(8):753-765
• Memorial Sloan Kettering Cancer Center. Forskolin. Integrative Medicine: About Herbs, Botanicals & Other Products. Available at: https://www.mskcc.org/cancer-care/integrative-medicine/herbs/forskolin
• Drugs.com. Forskolin Uses, Benefits & Dosage. Available at: https://www.drugs.com/npp/forskolin.html
• Medscape Reference. Coleus forskohlii, colforsin (forskolin) — dosing, indications, interactions, adverse effects. Available at: https://reference.medscape.com/drug/coleus-forskohlii-colforsin-forskolin-344584
• Ayurvedic Pharmacopoeia of India. Part I. Government of India, Ministry of Health and Family Welfare, Department of AYUSH

Connections

• Unique pharmacological niche: Forskolin is the only known natural direct activator of adenylyl cyclase. No other medicinal herb shares this specific mechanism. This makes it fundamentally different from herbs that achieve similar downstream effects (bronchodilation, vasodilation, lipolysis) through receptor-mediated pathways.
• Compare with ginkgo (EGb 761): Both are used for conditions involving vascular tone, but ginkgo works primarily through PAF antagonism, nitric oxide enhancement, and antioxidant activity — entirely different upstream mechanisms despite some overlapping downstream effects (vasodilation, antiplatelet activity).
• Compare with bacopa: Both are Ayurvedic-origin herbs that lack European regulatory monographs but have modern clinical trial evidence. Bacopa acts through cholinergic and neurotrophic mechanisms (AChE inhibition, BDNF upregulation) with no connection to the cAMP pathway. Their “cognitive support” category overlap is incidental — bacopa supports memory and cognition directly, while forskolin’s categorization here relates to broader neurometabolic support.
• Compare with holy basil (Tulsi): Fellow Lamiaceae family member and Ayurvedic herb with adaptogenic and anti-inflammatory properties, but working through entirely different mechanisms (eugenol, ursolic acid, cortisol modulation). No cAMP involvement.
• Compare with ashwagandha: Both are prominent Ayurvedic herbs with modern clinical interest. Ashwagandha acts through withanolide-mediated GABAergic, cortisol-modulating, and thyroid-modulating pathways — no overlap with adenylyl cyclase activation. Both have been studied for body composition, but through different mechanisms (ashwagandha via cortisol reduction and testosterone support; forskolin via direct cAMP-mediated lipolysis).
• Pharmaceutical comparisons: Forskolin’s bronchodilatory mechanism is analogous to beta-2 agonists (salbutamol) but achieved through direct AC activation rather than receptor-mediated stimulation. Its IOP-lowering effect is mechanistically distinct from all existing glaucoma drug classes. The intravenous derivative colforsin daropate is an approved cardiac inotrope in Japan, representing the most advanced pharmaceutical development of the forskolin scaffold.
• cAMP as a universal mediator: The breadth of forskolin’s pharmacological effects illustrates the central role of the cAMP/PKA signaling cascade in mammalian physiology. This universality is both its strength (broad therapeutic potential) and its limitation (lack of tissue selectivity when administered systemically).