Benefits
Body fat measured by DXA scan in overweight men
In a 12-week placebo-controlled trial in 30 overweight and obese men, 250 mg of a 10% forskolin extract twice daily lowered body fat percentage and fat mass on DXA scans compared with placebo; the rise in lean mass was only a trend. This is one small trial, and the same dose did not change body fat in women or in dieting adults.
Body composition and appetite ratings in overweight women
In a 12-week double-blind trial in mildly overweight women taking ForsLean at the same dose, fat mass and body fat did not differ from placebo. The extract group tended to gain less weight and reported less hunger and fullness. Results were reported for only 19 women, and the authors concluded the extract does not appear to promote weight loss.
Body weight and waist size in a 60-adult trial
In a 12-week placebo-controlled trial in 60 overweight adults, most of them women, the extract group lost about 1.9 kg and 1.8 cm of waist versus about 1.0 kg and 1.0 cm on placebo. Allocation was quasi-random rather than truly random, two authors work for the extract's maker, and the tables contain errors, so the result is uncertain.
Insulin levels alongside a reduced-calorie diet
In a 12-week placebo-controlled trial in 30 overweight adults who were all following a reduced-calorie diet, fasting insulin and an insulin-resistance score improved more with the extract than with placebo. Fasting blood sugar, weight and waist did not differ between groups, and on one diet questionnaire the extract group reported eating less. This is a single small trial.
Free testosterone in overweight men
In the same 30-man trial that reported lower body fat, serum free testosterone rose compared with placebo, but total testosterone did not differ significantly between groups. A later systematic review of herbs and testosterone found only some evidence for this root extract. The finding has not been repeated in another trial.
Mechanism of action
Raises cyclic AMP in cells
Forskolin switches on adenylyl cyclase, the enzyme that makes the cell messenger cyclic AMP. In fat cells in the lab, more cyclic AMP is linked to fat breakdown, which is the idea behind its weight-loss marketing. Trials have not shown that oral doses produce this effect in a way that leads to lasting weight loss.
Speeds up liver drug-processing enzymes in animals
In mice, the whole root extract increased liver enzymes that break down drugs, including the CYP2C enzyme that clears warfarin, and switched on the CYP3A4 gene in cell tests. In ordinary mice pure forskolin had much weaker effects than the extract, but in mice given human-type drug metabolism forskolin itself raised CYP3A4 gene activity. This has not been measured in people.
Reduces platelet clumping in the lab
In human platelet samples in the test tube, forskolin reduced platelet aggregation, and some prescription drugs strengthened the effect. Whether supplement doses do this in the body is unknown, but it is the basis for bleeding cautions.
Clinical trials
Randomized, double-blind, placebo-controlled trial of 250 mg Coleus forskohlii extract (10% forskolin) twice daily for 12 weeks, measuring body composition by DXA, testosterone, metabolic rate and blood pressure (Godard et al. 2005, Obes Res)
30 overweight and obese men with BMI of 26 or more (15 extract, 15 placebo).
Body fat percentage and fat mass fell significantly versus placebo and bone mass changed versus placebo. Lean mass rose only as a trend (p = 0.097). Free testosterone rose versus placebo; total testosterone changes (+16.8% vs -1.1%) were not significantly different. A small, single trial.
Double-blind randomized placebo-controlled trial of ForsLean, 250 mg of 10% extract twice daily for 12 weeks, measuring DXA body composition, blood safety markers and side effects (Henderson et al. 2005, J Int Soc Sports Nutr)
23 mildly overweight women enrolled; results reported for 7 on the extract and 12 on placebo.
No significant differences in fat mass (p = 0.16), fat-free mass or body fat percentage (p = 0.40). The extract group tended to gain less weight (p = 0.10) and reported less hunger and fullness. No clinically significant changes in blood tests, thyroid hormones, heart rate or blood pressure. The authors concluded it does not appear to promote weight loss.
Randomized, double-blind, placebo-controlled trial of 250 mg extract (10% forskolin) twice daily before meals for 12 weeks, with all participants advised to eat about 500 kcal a day less; the extract and placebo were made and supplied by Olive Life Sciences, India (Loftus et al. 2015, Nutrients)
41 overweight or obese adults enrolled in Australia; 30 completed (24 women, 6 men).
Weight, BMI and other body measurements did not differ from placebo; waist, hip and HDL changes occurred in both groups, likely from the diet. Fasting insulin (p = 0.001) and insulin resistance (p = 0.01) improved versus placebo, while fasting blood sugar did not change. Two people on the extract had loose stools or more frequent bowel movements in the first three weeks.
Double-blind, placebo-controlled, quasi-randomized trial of 250 mg Coleus forskohlii extract (10% forskolin, Forcslim) twice daily before meals for 12 weeks on participants' usual diet (Channangihalli Thimmegowda et al. 2026, J Int Soc Sports Nutr)
60 overweight adults aged 20 to 70 in India (30 per group), mostly women.
Per the paper's tables, weight fell about 1.9 kg with the extract versus about 1.0 kg with placebo, and waist about 1.8 cm versus 1.0 cm; the authors report these differences as significant. Liver enzymes stayed within normal ranges, blood pressure and heart rate did not differ from placebo, and no adverse events were reported. The tables are internally inconsistent, and a pairwise group comparison listed for weight and waist was not significant. Allocation was not truly random. Two authors work in research and development at the maker, Star Hi Herbs, which prepared the product, yet the paper declares no funding and no conflict of interest. A correction has been published.