Forskolin, a chemical found in coleus, activates the enzyme adenylate cyclase.² This enzyme is a turnkey compound that initiates a cascade of critical events within every cell of the body. Adenylate cyclase and the chemicals it activates comprise a “second messenger” system that is responsible for carrying out the complex and powerful effects of hormones in the body. Stimulation of the second messenger system by forskolin leads to blood vessel dilation,³ inhibition of allergic reactions,⁴ and an increase in thyroid hormone secretion.⁵ Forskolin has other properties as well, including inhibition of the pro-inflammatory substance known as platelet-activating factor (PAF)⁶ and inhibition of the spread of cancer cells.⁷

Studies in healthy humans, including at least one double-blind trial, have shown that direct application of an ophthalmic preparation of forskolin to the eyes lowers eye pressure,^{8, 9} thus reducing the risk of glaucoma. Direct application of the whole herb to the eyes has not been studied and is not recommended.

Forskolin may help dilate blood vessels and improve the forcefulness with which the heart pumps blood. A preliminary trial found that forskolin reduced blood pressure and improved heart function in people with cardiomyopathy.¹⁰ It is unknown if oral coleus extracts would have the same effect. A small double-blind trial found that inhaled forskolin could decrease lung spasms in asthmatics.¹¹ It is unclear if oral ingestion of coleus extracts will provide similar benefits.