Forskolin (Coleus forskohlii)

What it is

Coleus forskohlii, known in English as Indian coleus, is a member of the mint family (Lamiaceae). The extract that has been used in Ayurvedic medicine for centuries is obtained from its roots. The best-known ingredient is forskolin, a diterpene. Commercial extracts are usually standardized to 10 percent forskolin, and the studies were conducted with exactly such extracts.

In research, forskolin is a widely used tool; its effect on the cell has been described since 1981. A water-soluble derivative called colforsin daropate is used in Japan for acute heart failure and is considered the first clinically available drug based on this principle. This shows that the mechanism can have an effect in humans. It does not mean, however, that capsules with root extract have the same effect.

How it is supposed to work

Forskolin switches on the enzyme adenylate cyclase directly, without the detour via a receptor. The enzyme forms cAMP, one of the most important messengers in the cell. In rat brain tissue, cAMP rose 35-fold with forskolin. In fat cells, cAMP drives the breakdown of stored fat; in the airway muscles it relaxes, in the heart it strengthens contraction. From this come the ideas of using forskolin against overweight, asthma or raised intraocular pressure.

The open question is the dose in the body. In the laboratory, forskolin acts at concentrations of 5 to 10 µM. How much of it reaches the blood and fat tissue after swallowing a capsule has barely been studied in humans; we did not find any reliable measurements. A second mechanism is better supported than one would like: forskolin activates the pregnane X receptor, a switch for liver enzymes that break down medications.

What users are looking for

Most people take forskolin to lose weight, often as a fat-burner capsule, some also because of the possible effect on testosterone and muscle mass. User reports frequently mention a flatter stomach and less hunger; others notice nothing at all. These are uncontrolled reports. Less hunger fits one of the studies; the flatter stomach also occurred with placebo in another study, because all participants were dieting.

What the studies show

The study in men

30 overweight and obese men received 250 mg of extract with 10 percent forskolin or placebo twice daily for 12 weeks, 15 per group. Measured by DXA, fat mass and body fat percentage decreased significantly more with forskolin, bone mass rose, and there was a trend for lean mass. Free testosterone rose significantly, total testosterone not significantly. The study is the most frequently cited on forskolin, but very small.

The study in women

23 mildly overweight women took the same product or placebo for 12 weeks. They did not lose weight. With forskolin, weight tended to remain stable; with placebo it rose slightly; the difference was not significant. The women reported less hunger. Blood values, liver enzymes, thyroid hormones, pulse and blood pressure did not change. The study was partly funded by the manufacturer of the extract.

The diet study

30 overweight adults followed a calorie-reduced diet for 12 weeks and took 250 mg of extract or placebo twice daily. Waist and hips became narrower in both groups; weight did not differ. Insulin and insulin resistance improved only with the extract. However, insulin in the extract group was already higher at the start, which complicates the comparison. Two participants had softer stools in the first weeks.

Where the data stop

The evidence on weight loss is thin and contradictory. There are only four small controlled studies with 23 to 60 participants, none ran longer than 12 weeks, and we did not find a meta-analysis. One study found less fat, one no weight loss, one no difference in weight, and the most positive new study was only quasi-randomized, meaning the groups were not truly allocated at random. The testosterone finding rests on 15 men. Nobody has studied hard endpoints such as diabetes risk or heart health.

Beyond weight, too, much remains open. In asthma, in a study with 40 patients on 10 mg of forskolin daily, 40 percent of those treated had attacks, compared with 85 percent on cromoglicate; a second study with 60 adults, by contrast, found no better lung function; both were only single-blinded. Forskolin eye drops lowered intraocular pressure in one study; in another, aqueous humor flow remained unchanged. A study with 285 people found better sense of smell after COVID-19; confirmation is pending.

Status, approval and legal

The roots and aerial parts of Coleus forskohlii are classified in the EU Novel Food Catalogue as not novel in food supplements. Extracts may therefore be sold as food supplements without novel food authorization. No forskolin medicine is approved in Germany; the derivative colforsin daropate is a Japanese medicine. We did not find maximum levels from EFSA, the BfR or the German Nutrition Society (DGE). Health claims for plant compounds are mostly on hold in the EU; we did not find an authorized claim for forskolin. Forskolin is not on the WADA 2026 Prohibited List.

Safety

In the studies of up to 12 weeks, the extract was well tolerated; pulse, blood pressure, liver and thyroid values remained unchanged. The most common side effect is diarrhea: in a Japanese survey, 10.5 percent of users reported complaints, almost all gastrointestinal, and the more extract, the more frequent the diarrhea. The researchers considered less than 250 mg of extract per day to be safe and 500 mg to be probably acceptable. In mice, the extract caused dose-dependent liver damage, whereas pure forskolin did not; other ingredients are probably responsible. More important in practice are interactions: forskolin upregulates liver enzymes such as CYP3A4, and in mice the extract weakened the effect of the blood thinner warfarin. Anyone taking medications, especially anticoagulants, should discuss this with a doctor beforehand. There are no data for pregnancy and breastfeeding.

Sources

• Godard et al., Obes Res 2005 – forskolin in overweight men
• Henderson et al., J Int Soc Sports Nutr 2005 – Coleus forskohlii in overweight women
• Loftus et al., Nutrients 2015 – Coleus extract with a calorie-reduced diet
• Channangihalli Thimmegowda et al., J Int Soc Sports Nutr 2026 – Coleus extract and body weight
• Seamon et al., Proc Natl Acad Sci USA 1981 – forskolin activates adenylate cyclase
• Ding and Staudinger, J Pharmacol Exp Ther 2005 – forskolin, PXR and CYP3A
• Virgona et al., J Appl Toxicol 2013 – liver effects of Coleus extract in mice
• Nishijima et al., Nutrients 2019 – side effects of Coleus extract in Japan
• González-Sánchez et al., J Int Med Res 2006 – forskolin and asthma attacks
• EU Novel Food Catalogue – Coleus forskohlii