Coleus is best known for producing forskolin, a compound that raises levels of a cellular messenger called cyclic AMP, which influences fat metabolism, blood pressure, airway function, and eye pressure. Of the roughly 150 species in the coleus genus, only one, Coleus forskohlii, contains forskolin. The colorful coleus plants sold at garden centers are different ornamental species with no medicinal value. When you see “coleus” on a supplement label, it refers specifically to an extract of the forskohlii root.
How Forskolin Works in the Body
Forskolin directly activates an enzyme called adenylate cyclase, which produces cyclic AMP (cAMP). Think of cAMP as an internal signal that tells cells to get moving: it triggers fat cells to release stored energy, relaxes smooth muscle in blood vessels and airways, and influences hormone production. Most substances that raise cAMP do so indirectly by working through receptors on the cell surface. Forskolin bypasses those receptors entirely and switches on the enzyme itself, which is why researchers have studied it across so many different body systems.
Body Composition and Weight
Coleus supplements are marketed heavily for weight loss, but the evidence is mixed. In a 12-week trial of overweight and obese men taking 250 mg of a 10% forskolin extract twice daily, body fat percentage and fat mass decreased significantly compared to placebo, and lean body mass trended upward. A separate study in mildly overweight women using the same protocol found no significant differences in fat mass, lean mass, or body fat percentage between the supplement and placebo groups.
The takeaway: forskolin may help shift body composition in some populations, particularly men, but it is not a reliable standalone weight loss tool. The male-only benefit could relate to forskolin’s hormonal effects, discussed below.
Testosterone in Men
In that same 12-week male study, free testosterone levels increased significantly in the forskolin group compared to placebo. Total testosterone rose by about 17% on average in the supplement group, though that change didn’t reach statistical significance on its own. The increase in free testosterone, the form your body can actually use, is the more relevant finding. This hormonal shift likely contributed to the favorable changes in body composition seen in the male participants.
Respiratory and Asthma Support
Because cAMP relaxes smooth muscle, forskolin acts as a bronchodilator, opening the airways in a similar way to some asthma medications. In a six-month study of 20 asthma patients taking 10 mg of oral forskolin daily, the results in lung function measurements were comparable to those seen with sodium cromoglycate, a standard inhaled asthma drug. Additional smaller studies have confirmed that forskolin capsules at the same dose facilitate bronchodilation in asthma patients. The effect makes physiological sense: elevated cAMP in bronchial smooth muscle reduces the airway reactivity that triggers asthma attacks.
Eye Pressure and Glaucoma
Forskolin applied topically to the eye as a 1% suspension reduced aqueous fluid flow by 51% in animal studies. In human eyes, that same formulation produced a 35% reduction in outflow pressure, matched by a corresponding drop in fluid flow. Because elevated eye pressure is the primary risk factor for glaucoma, these findings have drawn interest as a potential complementary approach. The research here used eye drops, not oral supplements, so swallowing a capsule is unlikely to deliver the same targeted effect.
Cardiovascular Effects
Forskolin relaxes blood vessel walls, which lowers both the pressure the heart pumps against and the pressure in the veins returning blood to the heart. In patients with a type of heart failure called idiopathic congestive cardiomyopathy, forskolin reduced systolic, diastolic, and mean pulmonary artery pressure by more than 50%. Cardiac stroke volume, the amount of blood pumped per heartbeat, increased by roughly 70%. Heart rate rose only slightly. These were clinical settings using carefully controlled doses, but the data illustrates how potent forskolin’s vascular effects can be.
Typical Supplement Dosing
Most clinical trials have used 250 mg of coleus root extract standardized to 10% forskolin, taken twice per day. That delivers about 50 mg of actual forskolin daily. Supplements vary widely in their forskolin concentration, so checking the label for the standardization percentage matters more than the total milligram weight of the extract.
Safety and Drug Interactions
Because forskolin lowers blood pressure, it can amplify the effects of medications that do the same thing: beta-blockers, calcium channel blockers, and other vasodilators. If you already take blood pressure medication, adding coleus could push your pressure too low.
Forskolin also reduces the effectiveness of the blood thinner warfarin by speeding up its breakdown in the liver. It does this by boosting the activity of specific liver enzymes (CYP2C and CYP3A) that metabolize drugs. That same enzyme-boosting effect could increase the breakdown rate of other medications processed through the CYP3A pathway, a broad category that includes many common prescriptions from statins to certain antifungals.
The blood pressure-lowering and blood-thinning interactions are the most clinically relevant concerns. People with already low blood pressure or those on anticoagulant therapy should be especially cautious. In the clinical trials on body composition, no serious adverse events were reported at the standard dosing of 250 mg of 10% extract twice daily over 12 weeks.