A member of the mint family, Coleus forskohlii grows wild on the mountain slopes of Nepal, India, and Thailand. In traditional Asian systems of medicine, it was used for a variety of purposes, including treating skin rashes, asthma, bronchitis, insomnia, epilepsy, and angina. But modern interest is based almost entirely on the work of a drug company, Hoechst Pharmaceuticals.

Like other drug manufacturers, Hoechst regularly screens medicinal plants in hopes of discovering new medications. In 1974, work performed in collaboration with the Indian Central Drug Research Institute found that the rootstock of Coleus forskohlii could lower blood pressure and decrease muscle spasms. Intensive study identified a substance named forskolin that appeared to be responsible for much of this effect.

Like certain drugs used for asthma, forskolin increases the levels of a fundamental natural compound known as cyclic AMP.1,2 Cyclic AMP plays a major role in many cellular functions, and some drugs that affect it relax the muscles around the bronchial tubes.

The scientific evidence for the herb Coleus forskohlii as a treatment for any disease is weak. What is known relates to the substance forskolin rather than the whole herb.

Two preliminary controlled studies have found that oral forskolin may be beneficial for treatment of asthma.10,14Forskolin may work by stabilizing the cells that release histamine and other inflammatory compounds.3, as well as by relaxing smooth muscle tissue.4,5

Based on these apparent effects, Coleus forskohlii has been suggested as a useful treatment for eczema and other allergic conditions, dysmenorrhea (menstrual cramps), angina, irritable bowel syndrome (spastic colon), crampy bladder pain (as in bladder infections), and hypertension (high blood pressure). However, there is no direct evidence that it works.

One small double-blind study indicates that a concentrated forskolin extract might increase the rate of "fat burning," thereby potentially enhancing weight loss.12 In addition, forskolin eyedrops have shown promise in improving glaucoma.11

Coleus forskohlii has also been proposed as a treatment for psoriasis, because that disease appears to be at least partly related to low levels of cyclic AMP in skin cells.