This attractive, perennial member of the mint (Lamiaceae) family originated in the lower elevations of India. It is now grown around the world as an ornamental plant. The root is used medicinally.
Forskolin, a chemical found in coleus, activates the enzyme adenylate cyclase. [J Cyclic Nucleotide Res 1981;7: pp.201-24 (review)] 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 [Stroke 1986;17: pp.1299-303], inhibition of allergic reactions [Agents Actions 1986;18: pp.96-9] and an increase in thyroid hormone secretion. [Exp Cell Res 1990;172: pp.282-92] Forskolin has other properties as well, including inhibition of the pro-inflammatory substance known as platelet-activating factor (PAF) [Eur J Pharmacol 1993;245: pp.55-61] and inhibition of the spread of cancer cells. [Int J Cancer 1983;32: pp.801-4]
Coleus extracts standardized to 10 to 18% forskolin are available. While some doctors expert in herbal medicine recommend 50-100mg two to three times per day of standardized coleus extract, these amounts are extrapolations and have yet to be confirmed by direct clinical research. Most studies have used injected forskolin, so it is unclear if oral ingestion of coleus extracts will provide similar benefits in the amounts recommended above. Until ophthalmic preparations of coleus or forskolin are available, people with glaucoma should consult with a skilled healthcare practitioner to obtain a sterile fluid extract for use in the eyes.
Few adverse effects of coleus have been reported.
Coleus should be avoided in people with ulcers, because it may increase stomach acid levels. Direct application to the eyes may cause transitory tearing, burning, and itching. The safety of coleus in pregnancy and breast-feeding is unknown.
Certain medications may interact with coleus:
Albuterol – Supportive interaction
Aspirin – Adverse interaction
Epinephrine – Supportive interaction
Salmeterol – Supportive interaction
Forskolin, found in coleus, may help dilate blood vessels and improve the forcefulness with which the heart pumps blood. A preliminary trial found that intravenous forskolin reduced blood pressure and improved heart function amongst people with cardiomyopathy [Arzneim Forsch 1987;37: pp.364-7]. It is unknown whether oral coleus extracts would have the same effect, but some herbalists recommend taking 200-600mg orally per day of a 10% forskolin extract.
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, thus reducing the risk of glaucoma. [Lancet 1983;1: pp.958-60, Klin Monatsbl Augenheilkd 1984;185: pp.522-6] Direct application of the whole herb to the eyes has not been studied and is not recommended.
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