Consider hot pepper spices. Mexican chili. Hot Hungarian paprika. Cayenne pepper powder. They all come from the fruits of a family of plants called capsicums. Use of capsicums as seasonings dates back to 7000 BC, according to Mexican artifacts. In 1841 the Swiss traveler Tschudi encountered meat spiced with peppers while traveling in Peru. He wrote that, after a few spoonfuls, “the mouth starts to burn like glowing coal.” Tschudi found that extracts of other native peppers, when applied to the skin, were strong enough to cause pain, reddening and blisters.
That hardly sounds like a description of something that would be valued as a medicine. But those same South American cultures that spiced their food with peppers also used extracts of the pepper as folk remedies. Because once the burning sensation wears off, the skin is left largely resistant to pain.
Not only primitive societies used peppers as a source of medicine. In 1850 a British medical newspaper recommended a drop or two of hot-pepper extract applied on cotton to a sore tooth as an instant remedy for toothache.
Despite the long history of pepper extract as a folk remedy, it is only lately that its pain-relieving qualities have come to be understood. Now, in a remarkable joining of folk medicine and 20th-Century science, hot peppers have become part of today’s pharmacopoeia. But there is an important distinction between the crude pepper extracts used in folk medicine and current pepper-derived medicines. Crude extracts, like the tincture of capsicum and capsicum oleoresin that are still available today, are black, tarry preparations, which contain very little of the pepper’s active principle.
Modern medical uses are based on a single active ingredient called capsaicin that is purified from peppers and applied in a cream.
Capsaicin cream has been much appreciated by the first patients to benefit from it. Its initial use has been for the excruciating and often intractable pain of postherpetic neuralgia, a condition that can follow shingles and that, in the past, often required narcotic analgesics. According to Dr. Lawrence E. Millikan of the Tulane University Medical School, “Capsaicin cream is an order of magnitude better than anything we have used before for postherpetic neuralgia.”
The story of capsaicin is very much like that of another widely used and potent 20th-Century drug, aspirin. In folk medicine, fevers and headaches were treated with a tea made from the bark of the willow tree. Modern biochemists found that this tea contained an aspirin-like chemical that is effective for relief of fever, various aches and pains and arthritis, and that this compound acts by affecting a very important chemical system in the body, the prostaglandins.
Capsaicin’s effect was identified through one of the newest sciences, neuroscience, the study of the nervous system. A Hungarian researcher, Nicolaus Jansco, found that capsaicin blocks pain signals that come from nerves just under the skin. These nerves use a chemical messenger called substance P to transmit pain signals from injured tissues near the surface of the body to the brain. Capsaicin homes in on the stores of substance P and empties them from nerve endings in these peripheral tissues. That accounts for the initial burning sensation when capsaicin is applied to the skin. At the same time capsaicin prevents nerve cells from making more substance P. That’s why pain signals from tissues near the skin are greatly diminished or completely eliminated following continued application of capsaicin.
No other compound is known to do this.
What Jansco and others found established pepper extract as one of nature’s most astounding feats: a ready-made therapy for virtually any type of pain that originates in the skin. Dr. David Ross, a neurologist in North Miami Beach, Fla., has found that, “Capsaicin is an excellent drug for this type of pain.” Modern-day drug makers, with their bag of chemical tricks, could hardly have devised a more targeted treatment.
The first condition to benefit from capsaicin’s powers was postherpetic neuralgia (PHN). PHN occurs in about 20% of all people who have a bout of shingles, and in 50% of those over age 60 who have shingles. PHN makes discrete areas of skin extremely sensitive and painful, usually the skin of the torso or abdomen. The pain of PHN is relentless. Said Dr. Somamayaji Ramamurthy of the University of Texas, “It is well known that many patients with PHN attempt to commit suicide. They get very depressed.”
A large proportion of PHN patients are disabled to various degrees. “I have patients who basically walk around in their houses naked because they can’t stand clothes to touch the affected areas of their skin,” Ramamurthy said. These people also find it difficult to go out in public, to work, for instance.
Among the patients that Ramamurthy treated with the capsaicin cream, which is called Zostrix (manufactured by GenDerm), 75% were significantly improved by nine weeks. Only 30% of those treated with a placebo cream had any benefit. Maximum benefit from the Zostrix cream was not achieved until four weeks, so Ramamurthy warns his patients that they must continue to use it even if there is no apparent benefit at the outset.
A similar study, directed by Dr. Mark V. Dahl of the University of Minnesota, was reported in the August issue of the Journal of the American Academy of Dermatology. Dahl and his colleagues found that 54% of the PHN patients using Zostrix cream obtained 40% or greater relief of their pain, compared to only 6% of patients using a placebo cream.
Millikan describes one of his PHN patients as an example of the benefit of capsaicin cream. The patient, a 66-year-old man, had been treated with at least five different drugs with no benefit during the previous 18 months. These included a tranquilizer, an antidepressant, and several types of painkillers, including narcotics. Within two days of starting Zostrix the man experienced some decrease in discomfort, and by four weeks his pain was completely relieved.
Another pain condition that depends on release of substance P from nerves in the skin is diabetic neuropathy. In diabetic neuropathy there is a reduction in feeling in the feet and fingertips, and sometimes weakness of foot or hand muscles. Many patients with diabetic neuropathy have an unfamiliar kind of pain, which they describe as “crawling,” or “burning.” About half of diabetics ultimately fall victim to this condition.
Like PHN, diabetic neuropathy had been treated with analgesics, even including narcotics at times, as well as with antidepressant drugs, which are being used increasingly for pain treatment. But, said Dr. David Chad of the University of Massachusetts, “By and large, those of us who deal with these patients on a day-by-day basis are usually disappointed by these therapies.”
Since diabetic neuropathy arises by a nervous mechanism similar to PHN, capsaicin cream was also tested against diabetic neuropathy. Results of a five-center trial directed by Chad, in which 40 patients used Zostrix cream for four weeks, were presented in June at the American Diabetes Assn. meeting. Three out of every four patients reported obtaining pain relief, with pain being reduced by half in the average patient. Said Ross, who also helped run the trial, “I now tell patients that they have an 85% to 90% of getting off narcotics and getting back to aspirin or Tylenol.”
To achieve these results, patients must use Zostrix four times a day for at least four weeks, just as in PHN. But Chad finds that this is not a problem, since “These patients are highly motivated.”
What is particularly impressive about the benefit of capsaicin in patients with diabetic neuropathy is its remarkable specificity: Its effects are limited to blocking pain from the skin, so the diabetic patient doesn’t lose the sensitivity to touch and pressure that are so necessary for keeping the skin in healthy condition. “Capsaicin blocks ‘abnormal’ pain,” Chad said, “but it probably doesn’t interrupt the pain necessary for survival, so-called physiological pain.”