Forskolin is a compound derived from the roots of the Coleus forskohlii plant, also known as Plectranthus barbatus. It is known to increase levels of a chemical messenger in the body that can increase heart muscle contractions, relax smooth muscles, and may be involved in sugar and fat metabolism.
There are just two small clinical studies on the use of forskolin for weight loss, which, interestingly, found different effects in men and women. These are discussed in the Weight Loss Supplements Review.
There is also some evidence for other uses of forskolin, such as for preventing asthma attacks, as well as safety concerns about taking forskolin with certain medications. See the Encyclopedia article about Coleus forskohlii for information about these topics.