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Do Topical Herbal Agents Provide Pain Relief?

A randomized, placebo-controlled pilot study of chronic pain patients with fibromyalgia demonstrated a positive response to topical herbal agents for pain management.
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By the American College of Rheumatology (ACR) definition, fibromyalgia syndrome (FMS) is a syndrome of widespread muscle pain (over three months) and stiffness with 11 or more characteristic tender points (TePs) on palpation.1 It affects two percent of the population, predominantly females, with the most common age at presentation of 40 to 50 years.2

Fibromyalgia patients are high consumers of complementary/alternative medicine (CAM) interventions.3-5 In our survey of 116 physiatrists (rehabilitation medicine specialists) in Ontario, Canada, 55 percent of respondents agreed that FMS is a “real disabling condition.” When asked what type of alternative therapy works, 14 different types were mentioned; the top three were acupuncture, biofeedback, and chiropractic.6 In one survey of 72 FMS participants, the use of topical analgesic rubs was rated the highest in CAM products tried.7 Few studies have been published on the use of topical agents in FMS. This includes an uncontrolled, short follow-up (20 minutes) study of topical camphor, methyl salicylate, menthol lotion.8 Another double-blind study used topical capsaicin for chronic neck pain. Of those patients, 35 percent had FMS.9 To date, with our recent major invited review of the literature on FMS and alternative medicine use,10 there has been no published high quality randomized controlled trial on topical herbal agents for FMS pain.

In September 2004, the authors coordinated a clinical trial for FMS using a patented over-the-counter topical named O24 and consisting of a proprietary blend of six herbal oils: rosemary, peppermint, camphor, eucalyptus, aloe vera, and lemon/orange.

Each of these herbal agents have been studied in some detail, with effects summarized as follows:

Aloe vera. Studies suggest topical use is effective in psoriasis, burns, frostbite, genital herpes, radiation-induced skin toxicity (delayed onset). The aloe gel is found in the inner portion of the aloe leaf. Its active constituents include aloe emodin anthrone, dithranol, chrysarobin and allantoin. Pain producing transmitters such as (1) bradykinin is inhibited by the carboxypeptidase and salicylate components; (2) histamine inhibited by magnesium lactate component. Another component C-glucosyl chromone reduces topical inflammation. It may also inhibit a potent vasoconstrictor thromboxane A2 and thus increase microcirculation to prevent ischemia in the wound area and speed the healing of burns and frostbite. Antibacterial and antifungal properties have also been documented. Potential adverse effects/ interactions include lowering of blood glucose (when taken orally).

Eucalyptus. Studies suggest effectiveness in inflammation of respiratory tract mucous membranes, rheumatic complaints and nasal stuffiness. The oil contains 40-85 percent eucalyptol (1,8-cineole) which, by stimulating saliva production, will activate the swallowing reflex and suppress an impending cough. As a topical, it works as a mild counterirritant and may inhibit prostaglandin synthesis. Potential adverse effects/interactions with oral use include nausea, vomiting, diarrhea. The ingestion of 3.5 ml of the oil alone can be fatal (delirium, convulsions). Inhibition of cytochrome P450 1A2/ 2C19/ 2C9/ 3A4 may increase drug levels but this has not been reported yet in humans. It’s oral use is contraindicated in gastrointestinal and bile duct inflammation, severe liver disease, kidney inflammation and hypotension.

Rosemary. Studies suggest effectiveness for preventing baldness, alopecia areata, toothache, eczema, myalgia, sciatica, intercostals neuralgia, and as an insect repellant. The dried leaves contain 1-2.5 percent essential oil which consists primarily of cineole, borneol, camphor and pinenes. The oil has a spasmolytic effect on smooth muscle and may also have a positive inotropic effect on the heart. Topical use may irritate the skin and increase blood flow. It also has antibacterial, antifungal and antioxidant properties. Potential adverse effects/ interactions with topical use include photosensitivity, erythema and dermatitis. Occupational asthma has also been reported. With oral use, it may stimulate uterine and menstrual flow and is therefore not recommended in pregnancy.

Camphor. Studies on topical use suggest usefulness in osteoarthritis, warts, cold sores, hemorrhoids. It is used topically as an analgesic and antipruritic. It is also used in inhalation therapy as an antitussive and orally as an expectorant, and antiflatulent. It is safe when used in low concentrations 0.1-11 percent for topical use on intact skin. The applicable part of camphor is the wood distillate. Its counterirritant action is due to vasoconstriction which leads to the activation of reflex mechanisms resulting in improved local circulation. Adverse effects occur with improper oral use. Significant toxicity (respiratory failure, status epilepticus) has been documented with as little as two grams in adults and 700 mg in children. Topical use is therefore not recommended in infants and should not be applied around the mouth. Oral use is not recommended as well in adults.

Peppermint. Studies indicate topical usefulness in headache, myalgia, post-herpetic neuralgia, toothache, oral mucosa inflammation, pruritis, urticaria and as an antibacterial, antiviral agent for repelling mosquitoes. Orally, the oil is used for colds, coughs, irritable bowel syndrome, dyspepsia, dysmenorrhea. The oil is obtained by steam distilling the fresh above-ground parts of the flowering plant. It contains 28-28 percent menthol, 20-31 percent menthone and 3-10 percent methyl acetate. Its topical action is as a counterirritant. It has in vitro antibacterial and antiviral effects. It also increases salivation, thus inhibiting the cough reflex and orally, via direct smooth muscle relaxing effects, it works as an antispasmodic. Adverse reactions from topical use include skin irritation and contact dermatitis. Application to the face, nasal, chest areas of babies, small children can cause laryngeal and bronchial spasms leading to respiratory collapse. Potential interactions include inhibiting CYP1A2, 2C9, and 3A4 enzymes (not yet documented in humans).

Last updated on: January 28, 2012
First published on: January 1, 2006