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Although I have been in practice for over 25 years, I have only recently come across Coleus (which is now known under another name since it has been categorised in the genus Plectranthus. For the sake of ease, and because this is name that it is generally used, I will refer to it as Coleus!) So far the plant is rather a mystery to me. Most of the research has been carried out on an isolated constituent known as forskolin and since it is not a widely used plant, there is little anecdotal evidence on the use of the whole plant available. Potentially, Coleus is an incredible healer! As I introduce it into my practice, hopefully I will obtain knowledge gained from experience to verify what follows...

Coleus is an Ayurvedic herb, a small perennial member of the mint family which can be found growing in subtropical areas in India, Nepal, Burma, Thailand and Sri Lanka. It has tuberous roots and bright green leaves and has a distinctly camphor-like aroma. It contains labdane diterpenes (including forskolin) and essential oil.[1] Its taste is pungent and from an Ayurvedic perspective, it has the ability to balance all three doshas.[2]

For centuries, the leaves and root of Coleus have been a traditional remedy in India for digestive complaints, heart and lung conditions, asthma, insomnia, muscle spasm, convulsions and skin disease.[3] Since the 1970s Coleus has been the subject of extensive research, due to the fact that forskolin isolated from the roots was found to have some incredible therapeutic effects.[3] In 1974 research carried out by Hoechst Pharmaceuticals and the Indian Central Drug Research Institute in a search for sources of new drugs in the medicinal plant world, found that extracts of Coleus root reduced muscle spasms and lowered blood pressure. They were led to the plant as it is related to Coleus amboinicus, a herb used in Ayurvedic medicine for colic, asthma, chronic coughs, calculus, strangury, epilepsy, fevers, convulsions, piles and dyspepsia. The fresh juice was applied round the eye to relieve conjunctivitis.[4] On further investigation, the chemical component known as forskolin was isolated from Coleus forskohlii, and thought to be responsible for these actions. Forskolin has now become available as a prescription drug and a supplement and is recommended in the treatment of hypothyroidism, allergies, asthma, eczema, psoriasis, obesity, glaucoma and for conditions associated with muscle spasm including spastic colon, hypertension, angina and bladder pain.[3]

Further studies have revealed that the main action behind the effects of forskolin is the activation of an important enzyme that raises levels of cyclic adenosine monophosphate, (cAMP). CAMP is a very important cell-regulating compound which acts as a 'second messenger' altering a variety of membrane transport proteins and thereby activating many other enzymes involved in a whole range of cellular functions including hormone activation. By increasing cAMP, forskolin has been shown to have a wide array of benefits particularly in the circulatory system, the respiratory tract, the digestive system, the immune system, the skin and eyes.

In the circulatory system forskolin inhibits platelet activity, decreasing the risk of blood clotting; it increases the force of the contraction of heart muscle thereby improving heart function, making it worth using it for patients with angina and congestive heart failure. By relaxing arteries and other smooth muscle, it can help to lower blood pressure by dilating blood vessels.[3]

It has an immunomodulatory effect, activating macrophages and lymphocytes. As a potent platelet aggregation inhibitor it has been found to inhibit the melanoma-induced platelet aggregation, and tumour colonization, suggesting that Coleus could be a useful herb in the management of cancer by inhibiting tumour metastases.[5]

Coleus has great potential in the treatment of allergies because allergic conditions such as asthma, eczema, and hay fever are associated with low cAMP and high platelet activating factor (PAF) levels. Forskolin reduces histamine release and has been shown to inhibit production of substances that trigger the inflammatory response. It is recommended for treating inflammatory skin problems including eczema and can also be helpful in psoriasis, which seems to be partly related to the low levels of cAMP in skin cells [2,3]. It is potentially an excellent herb for treating asthma through its antihistamine action and its antispasmodic action on smooth muscle, giving it a bronchodilatory effect. Many drugs used for asthma apparently increase cAMP by inhibiting enzymes that break it down. So Coleus could be useful when weaning patients off conventional asthma treatments.

The relaxing effect of forskolin on smooth muscle means that Coleus can be used to treat conditions such as muscle tension and cramp, convulsions, muscle cramping and bladder pain.[3] It is used for colic caused by spasm in the GI tract and also has the ability to enhance secretion of digestive enzymes and promote good digestion.

Forskolin has also been shown to stimulate the release of thyroid hormone, relieving many symptoms associated with hypothyroidism, such as depression, fatigue, weight gain and dry skin. [3] It increases fat metabolism and insulin production, and improves energy. It has become a popular remedy for helping in the management of obesity. Interestingly obese people tend to have low levels of cAMP. By improving neurotransmitter function it may be useful in relieving depression.

Coleus has a specific use for glaucoma when applied topically as it has a reputation for decreasing intraocular pressure by reducing the flow of aqueous humour.[6].

The problem with whole plant extracts of Coleus is that so far, most of the research has been carried out on the isolated constituent forskolin, although some sources suggest that clinical results using the whole plant are better. The forskolin content of the root is generally 0.2-0.3% and it may not be enough to produce the desired effect. As a compromise perhaps, some recommend using standardized extracts to ensure sufficient forskolin, (50mg , ensuring 9mg of forskolin, 2 or 3 times daily), although it is worth considering that there may well be other constituents which support the actions of forskolin as is normally the case when using the whole plant. Nature knows better!  Referral back to the therapeutic effects of its relative Coleus amboinicus, which in many ways are similar, may suggest hopeful therapeutic benefits from the whole plant, despite their relatively low forskolin content. The current recommended doses are 5-10 gms daily of the dried root, 3-15 mls of 1:3 @25% tincture 3 times daily.

Although not much is know yet about herb drug interactions, forskolin is contraindicated in hypotension [1,2], peptic ulcer [1] and for patients taking prescribed medication, especially hypotensive and antiplatelet drugs.[1]
 

References:

1. Bone K. The Ultimate Herbal Compendium. Phytotherapy Press. Queensland. 2007.
2. Pole S. Ayurvedic Medicine. Elsevier. Philadelphia. 2006.
3. Foster S.  Johnson R. Desk Reference to Nature's Medicine. National Geographic Society. Washington D.C. 2006.
4. Narkarni Dr KM. Indian Materia Medica. Popular Prakashan Private Ltd. Mumbai. 1908.
5. Mishra LC. Scientific Basis for Ayurvedic Therapies. CRC Press. New York. 2003.
6. Bone K. Clinical Applications of Ayurvedic and Chinese Herbs. Phytotherapy Press. Queensland. 1996.