The handful of available randomized controlled trials exploring the effects of Coleus forskohlii on body weight and body composition have reported mixed results.
One trial found no effect of supplementation with 500 mg of Coleus forskohlii extract (containing 10% forskolin, the main bioactive compound in Coleus forskohlii) daily for a period of 12 weeks on body weight or body composition in women with overweight.[1] On the other hand, a 12-week trial conducted in men with overweight/obesity found that the same supplementation protocol resulted in large reductions in fat mass (−4.5 kg) and body fat percentage (−4%).[2] Finally, the most recent trial examined the effects of the aforementioned supplementation protocol over a period of 12 weeks in adults (24 women; 6 men) with overweight/obesity and found no effects on body weight or body composition.[3]
Whereas the trials above explored the effects of Coleus forskohlii taken orally, one 1987 trial looked at the effects of the topical application of forskolin.[4] In this trial, 4 women who were on a very-low-calorie diet applied a forskolin-containing cream on one of their thighs, with the opposite thigh treated with a placebo cream daily for 4 weeks. At the end of the trial period, there was a 1-cm greater reduction in thigh circumference in the forskolin group than in the placebo group.
Taken together, the findings above suggest either no effects of oral supplementation with Coleus forskohlii on body weight and body composition or gender-specific effects, with potential improvements in men with overweight/obesity but not in women with overweight/obesity. The findings also suggest that the topical application of forskolin may promote regional fat loss. That said, much more research is needed before firm conclusions can be drawn.