Coleus

The root has been used in Hindu and Ayurvedic medicine for high blood pressure, congestive heart failure, eczema, colic, respiratory disorders, painful urination, insomnia and convulsions ^{31Reference 31Coleus forskohlii · 2006ReviewAlternative Medicine Review, 11(1), 47–51. https://pubmed.ncbi.nlm.nih.gov/16597194/View study →}. Coleus species are also recorded in Ayurvedic use for heart disease and spasmodic pain ^{22Reference 22Dubey MP et al. · 1981AnimalPharmacological studies on coleonol, a hypotensive diterpene from Coleus forskohlii — [animal model]View study →}.

In India the tuberous roots are also eaten as a condiment, often prepared as a pickle ^{35Reference 35Fern · 2026Plectranthus barbatus — habit, range, habitat, edible and medicinal uses, hazards — species databaseView study →}. The plant is used to break fevers in India as well ^{35Reference 35Fern · 2026Plectranthus barbatus — habit, range, habitat, edible and medicinal uses, hazards — species databaseView study →}.

In Brazil the plant is commonly used as a painkiller, for malaria, and for liver and stomach complaints ^{35Reference 35Fern · 2026Plectranthus barbatus — habit, range, habitat, edible and medicinal uses, hazards — species databaseView study →}.

In East Africa the plant is used to break fevers ^{35Reference 35Fern · 2026Plectranthus barbatus — habit, range, habitat, edible and medicinal uses, hazards — species databaseView study →}.

This is the indication with the most direct human testing, though never with the whole herb. In rabbits, forskolin injected into the eye raised cyclic AMP in the iris and ciliary body, roughly doubled the outflow of fluid from the eye, and lowered intraocular pressure (IOP) by about 5 mm Hg at four hours ^{12Reference 12Bartels SP et al. · 1982AnimalForskolin stimulates cyclic AMP synthesis, lowers intraocular pressure and increases outflow facility in rabbits — [animal model]View study →}.

In people, three studies tested oral forskolin as an add-on to standard therapy. In an open, case-controlled study across eight Italian glaucoma centres, 97 patients on maximum medical therapy and awaiting surgery took a forskolin-plus-rutin supplement or continued their drops alone. IOP fell a further 10% in the supplement group within a week, and 15% in those who started at 21 mm Hg or higher; the control group stayed stable ^{9Reference 9Vetrugno M et al. · 2012ObservationalOral administration of forskolin and rutin contributes to intraocular pressure control in primary open angle glaucoma patients under maximum tolerated medical therapy — [open case-controlled study]View study →}.

A small randomised pilot study in 22 patients tested a tablet combining a coleus root extract with homotaurine, carnosine, folic acid, B vitamins and magnesium for a year. IOP fell further, and retinal function measures improved, in the supplement group ^{10Reference 10Mutolo MG et al. · 2016RCTOral administration of forskolin, homotaurine, carnosine, and folic acid in patients with primary open angle glaucoma — [randomised controlled trial]View study →}.

In ten patients having laser iridotomy, a week of forskolin and rutin beforehand prevented the rise in eye pressure seen after the procedure with placebo ^{11Reference 11Nebbioso M et al. · 2012Clinical trialForskolin and rutin prevent intraocular pressure spikes after Nd:YAG laser iridotomy — [clinical trial]View study →}.

Gap: every product combined forskolin with other actives, all three studies were add-ons to existing glaucoma treatment, and none tested the root itself.

The two human trials used the marketed preparation, a root extract standardised to 10% forskolin (ForsLean), at 250 mg twice daily for 12 weeks.

In 30 overweight and obese men (15 per group), the extract lowered body-fat percentage and fat mass on DXA scans compared with placebo. It also raised free testosterone and bone mass, with a non-significant trend toward more lean mass ^{4Reference 4Godard MP et al. · 2005RCTBody composition and hormonal adaptations associated with forskolin consumption in overweight and obese men — [randomised, placebo-controlled trial]View study →}.

In 23 mildly overweight women, the extract did not reduce fat mass or body fat. It showed a non-significant trend toward less weight gain, and the women taking it reported less hunger and fullness ^{5Reference 5Henderson S et al. · 2005RCTEffects of Coleus forskohlii supplementation on body composition and hematological profiles in mildly overweight women — [randomised, placebo-controlled trial]View study →}.

Forskolin stimulates fat breakdown in isolated rat fat cells ^{6Reference 6Okuda H et al. · 1992AnimalRelationship between cyclic AMP production and lipolysis induced by forskolin in rat fat cells — [animal model]View study →}. In obese mice, a standardised coleus extract increased fat breakdown and reduced fat accumulation, alone and combined with Garcinia indica ^{8Reference 8Tung YC et al. · 2021AnimalColeus forskohlii and Garcinia indica extracts attenuated lipid accumulation by regulating energy metabolism and modulating gut microbiota in obese mice — [animal model]View study →}. An earlier set of trials applied forskolin to the thigh as an ointment, so it does not bear on the oral herb ^{7Reference 7Greenway FL et al. · 1995Clinical trialTopical fat reduction — [clinical trial]View study →}.

Gap: the two trials disagree by sex, both are small, and neither has been repeated.

Forskolin relaxes airway smooth muscle through cyclic AMP, the same pathway β-agonist inhalers use. In a randomised, double-masked, placebo-controlled crossover in 16 asthma patients, a single 10 mg inhaled dose of forskolin (colforsin) produced measurable bronchodilation. Its effect on airway conductance was smaller than that of the β-agonist fenoterol, and it caused less tremor ^{15Reference 15Bauer K et al. · 1993RCTPharmacodynamic effects of inhaled dry powder formulations of fenoterol and colforsin in asthma — [randomised, placebo-controlled trial]View study →}.

In a single-blinded trial in 40 children and adults with mild or moderate persistent asthma, oral forskolin (10 mg a day for six months) was compared with inhaled sodium cromoglycate. Fewer patients had asthma attacks on forskolin (8 of 20) than on cromoglycate (17 of 20), while lung-function measures were similar in both groups ^{16Reference 16González-Sánchez R et al. · 2006RCTForskolin versus sodium cromoglycate for prevention of asthma attacks: a single-blinded clinical trial — [randomised controlled trial]View study →}.

In guinea pigs, intravenous or intratracheal forskolin prevented and reversed allergic bronchospasm and blocked leukotriene and histamine release from lung tissue ^{18Reference 18Kreutner W et al. · 1985AnimalBronchodilator and antiallergy activity of forskolin — [animal model]View study →}. A coleus extract reduced airway inflammation and remodelling in sensitised guinea pigs and rats ^{17Reference 17Ma C et al. · 2019AnimalExtracts of Coleus forskohlii relieves cough and asthma symptoms via modulating inflammation and the extracellular matrix — [animal model]View study →}.

Gap: the clearest bronchodilation came from inhaled pure forskolin, and no trial compares oral coleus with modern controller therapy.

In isolated guinea-pig heart tissue, forskolin activated adenylate cyclase more strongly than isoprenaline and strengthened heart-muscle contraction ^{19Reference 19Metzger H · 1981The positive inotropic-acting forskolin, a potent adenylate cyclase activator — [ex vivo, animal heart tissue]View study →}. In membranes from failing human hearts, it activated adenylate cyclase about six times more than isoproterenol and kept its full activity, where β-agonists lose potency. It also strengthened contraction of failing human heart muscle ^{20Reference 20Bristow MR et al. · 1984In vitroPharmacology and inotropic potential of forskolin in the human heart — [in vitro]View study →}.

When forskolin was infused intravenously into 12 patients with severe (NYHA stage III) congestive cardiomyopathy, it lowered the load on the heart and cut pulmonary pressures by more than half, while cardiac output rose and stroke volume increased by about 70%. These effects were more pronounced than those of dobutamine or nitroprusside given alone ^{21Reference 21Baumann G et al. · 1990Clinical trialCardiovascular effects of forskolin (HL 362) in patients with idiopathic congestive cardiomyopathy — a comparative study with dobutamine and sodium nitroprusside — [clinical trial]View study →}.

Forskolin, first described as coleonol, also lowered blood pressure in cats and rats by relaxing blood-vessel muscle, and in small doses it strengthened heart contraction ^{22,32Reference 22Dubey MP et al. · 1981AnimalPharmacological studies on coleonol, a hypotensive diterpene from Coleus forskohlii — [animal model]View study →Reference 32Saksena AK et al. · 1985Identity of coleonol with forskolin: structure revision of a base-catalysed rearrangement product — [journal article]}.

Gap: every heart result comes from isolated tissue or intravenous infusion in a monitored setting. Nothing shows that the oral root affects the heart this way.

The cyclic AMP rise that relaxes airways also restrains inflammatory cells, and this has been shown in human cells. Forskolin inhibited antigen-induced histamine release from human basophils and lung mast cells in step with the rise in cyclic AMP ^{13Reference 13Marone G et al. · 1986In vitroForskolin inhibits the release of histamine from human basophils and mast cells — [in vitro]View study →}.

In human white blood cells, forskolin and isoforskolin reduced the inflammatory response to bacterial endotoxin, lowering TLR4, MyD88 and NF-κB levels and cytokines including IL-1β, IL-6 and TNF-α ^{14Reference 14Du X et al. · 2019In vitroIsoforskolin and forskolin attenuate lipopolysaccharide-induced inflammation through TLR4/MyD88/NF-κB cascades in human mononuclear leukocytes — [in vitro]View study →}. Forskolin also blocked allergic mediator release in guinea-pig lung ^{18Reference 18Kreutner W et al. · 1985AnimalBronchodilator and antiallergy activity of forskolin — [animal model]View study →}.

Gap: the evidence stops at isolated cells and animal tissue. No clinical trial has tested an allergic or inflammatory condition.

Cyclic AMP activates PKA and the transcription factor CREB, a pathway involved in forming long-term memory, and forskolin is a standard laboratory tool for switching it on.

In rats, forskolin injected directly into the brain had opposite effects at different concentrations. Up to 80 µM increased tau phosphorylation and impaired spatial memory, while 200 µM lowered tau phosphorylation and caused no memory deficit ^{24Reference 24Tian Q et al. · 2009AnimalBiphasic effects of forskolin on tau phosphorylation and spatial memory in rats — [animal model]View study →}. In zebrafish, forskolin injected into the abdomen for five days restored learning and memory after repeated low-oxygen exposure ^{25Reference 25Nguyen QTN et al. · 2024AnimalForskolin rescues hypoxia-induced cognitive dysfunction in zebrafish — [animal model]View study →}.

Gap: there is no human cognition data. The rat work injected forskolin into the brain, and at lower concentrations it impaired memory. Whether oral forskolin reaches the brain is unknown.

Cyclic AMP signalling affects cancer cell growth, migration and sensitivity to chemotherapy, and a narrative review has argued that forskolin deserves formal study as an anticancer agent ^{23Reference 23Sapio L et al. · 2017ReviewThe natural cAMP elevating compound forskolin in cancer therapy: is it time? — [review]View study →}.

Gap: the evidence is cell-line and review-level only, with no human data.

Tolerability. In the two 12-week trials of the 10% extract at 250 mg twice daily, the women’s trial found no clinically significant changes in blood markers, heart rate, blood pressure or reported side effects ^{4,5Reference 4Godard MP et al. · 2005RCTBody composition and hormonal adaptations associated with forskolin consumption in overweight and obese men — [randomised, placebo-controlled trial]View study →Reference 5Henderson S et al. · 2005RCTEffects of Coleus forskohlii supplementation on body composition and hematological profiles in mildly overweight women — [randomised, placebo-controlled trial]View study →}. Long-term use beyond 12 weeks has not been studied.

Blood pressure. Forskolin lowers blood pressure by relaxing blood-vessel muscle ^{22Reference 22Dubey MP et al. · 1981AnimalPharmacological studies on coleonol, a hypotensive diterpene from Coleus forskohlii — [animal model]View study →}. Take care alongside antihypertensive medicines and with existing low blood pressure ^{31Reference 31Coleus forskohlii · 2006ReviewAlternative Medicine Review, 11(1), 47–51. https://pubmed.ncbi.nlm.nih.gov/16597194/View study →}.

Bleeding. Forskolin inhibits platelet aggregation, so it is best avoided or used with care alongside anticoagulant medicines and in bleeding disorders ^{31Reference 31Coleus forskohlii · 2006ReviewAlternative Medicine Review, 11(1), 47–51. https://pubmed.ncbi.nlm.nih.gov/16597194/View study →}.

Stomach acid. Forskolin can increase stomach acid, so take care with peptic ulcers ^{31Reference 31Coleus forskohlii · 2006ReviewAlternative Medicine Review, 11(1), 47–51. https://pubmed.ncbi.nlm.nih.gov/16597194/View study →}.

Drug metabolism. In mice, a standardised extract with 10% forskolin raised the activity of several cytochrome P450 enzymes (mainly CYP2B, 2C and 3A) in the liver; pure forskolin had only a weak effect, so the induction comes mainly from other constituents ^{26Reference 26Virgona N et al. · 2012AnimalColeus forskohlii extract induces hepatic cytochrome P450 enzymes in mice — [animal model]View study →}. The enzymes returned to normal soon after the extract was stopped. A higher dose was needed to induce enzymes in the gut, and the authors judged gut-level drug interactions unlikely ^{27Reference 27Yokotani K et al. · 2020AnimalComparison of CYP induction by Coleus forskohlii extract and recovery in the small intestine and liver of mice — [animal model]View study →}. No human interaction study has been done.

Fatty liver. In mice with fatty liver disease, the extract weakened the benefit of a diet change and raised liver drug-metabolising enzymes ^{28Reference 28Suzuki S et al. · 2020AnimalColeus forskohlii extract attenuated the beneficial effect of diet-treatment on NASH in a mouse model — [animal model]View study →}.

Serious illness. Heart failure, glaucoma and asthma are conditions that need medical management, and forskolin’s heart effects have only been produced by intravenous infusion.