Benefits
Body fat and body composition
In a 12-week double-blind 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 and raised bone mass compared with placebo; lean mass rose only as a trend. In women taking ForsLean and in adults on a reduced-calorie diet, the same dose did not change body weight compared with placebo.
Thyroid hormones and metabolic rate
Forskolin is sometimes promoted for thyroid or metabolic support because it raises cAMP. In the 12-week trial of ForsLean in women, TSH, T3 and T4 showed no clinically significant changes compared with placebo. The men's trial listed metabolic rate as an outcome, but its published summary reports no result for it.
Free testosterone in men
In the 12-week trial in 30 overweight and obese men, serum free testosterone rose significantly compared with placebo. Total testosterone rose about 17% on the extract and fell about 1% on placebo, but that difference was not statistically significant. This single small trial has not been repeated, and the finding does not apply to women.
Mechanism of action
Adenylyl cyclase activation and cAMP
Forskolin directly activates adenylyl cyclase, the enzyme that makes cyclic AMP (cAMP), and raised cAMP sharply in rat brain tissue in early laboratory work. In isolated rat fat cells it raised cAMP and, at higher concentrations, increased lipolysis, the breakdown of stored fat. These are cell-level findings. In people, oral forskolin did not change body weight in two trials, and the body-composition and testosterone results come from one small trial in men.
Clinical trials
Randomized, double-blind, placebo-controlled 12-week trial of a Coleus forskohlii extract standardized to 10% forskolin, 250 mg twice daily (50 mg forskolin a day), the same specification as ForsLean. Outcomes included DXA body composition, testosterone, metabolic rate and blood pressure. (Godard et al. 2005, Obes Res)
30 overweight and obese men (BMI 26 or higher), 15 per group, over 12 weeks.
Body fat percentage and fat mass fell, and bone mass rose, compared with placebo. Lean body mass rose only as a trend (p = 0.097). Free testosterone rose significantly compared with placebo; total testosterone rose 16.77% versus a 1.08% fall on placebo, a difference that was not significant. The published summary reports no body-weight result, and later trials in women and in dieting adults found no weight difference from placebo.
Randomized, double-blind, placebo-controlled 12-week trial of ForsLean (250 mg of 10% Coleus forskohlii extract twice daily), funded in part by Sabinsa. Outcomes: DXA body composition, body weight, appetite and fatigue questionnaires, blood safety markers and hormones. (Henderson et al. 2005, J Int Soc Sports Nutr)
Mildly overweight women; results reported for 7 on ForsLean and 12 on placebo.
Fat mass, fat-free mass and body fat percentage did not differ from placebo. Body mass tended to rise less on ForsLean (-0.7 kg versus +1.0 kg, p = 0.10). The ForsLean group reported less hunger and fullness on questionnaires. No clinically significant changes were seen in blood lipids, liver and muscle enzymes, TSH, T3, T4, heart rate or blood pressure. The authors concluded it does not appear to promote weight loss.