Alkaloid

Many medically useful alkaloids act by way of the peripheral nervous system; others work directly on the brain. Prominent among the latter are the pain relievers morphine and codeine, derived from the opium poppy (Papaver somniferum). Morphine is the stronger of the two, but codeine is often prescribed for moderate pain. Codeine is also an effective cough suppressant; for years it was a standard component of cough syrups. Now, however, it has been replaced for the most part by drugs that do not have the psychological side effects of codeine.

Both morphine and codeine are addictive drugs that produce a state of relaxed, dreamy euphoria—an exaggerated state of "feeling good," referred to by drug addicts as a "high." The equivalent street drug is heroin, derived from morphine by a simple chemical modification. Heroin addicts typically believe that their drug is stronger and produces a more pronounced "high" than morphine; however, since heroin is rapidly converted to morphine once it enters the body, most medical scientists consider the two drugs completely equivalent.

The effects of cocaine are almost the opposite of those of morphine; cocaine's legal classification as a narcotic—a drug that produces stupor—is misleading from a medical standpoint. This product of the coca plant, native to the Andes Mountains in South America, produces a state of euphoric hyperarousal. The user feels excited, elated, and intensely aware of his or her surroundings, with an impression of enhanced physical strength and mental ability. These feelings are accompanied by the physical signs of arousal: elevated heart rate and blood pressure. The increased heart rate caused by a high dose may lead to fibrillation and death.

A cocaine "high," unlike the "highs" from most abused drugs, lasts less than half an hour—often much less. Once an individual becomes addicted, he or she needs large amounts of the expensive drug. Users' enhanced aggressiveness and physical self-confidence further increase cocaine's social dangers. Cocaine usage over time can result in paranoid schizophrenia, a type of insanity characterized by unfounded suspicion and fantasies of persecution; when this psychological condition is combined with continued cocaine use, the addict may perform violent acts against the supposed plotters.

Cocaine is also a local anesthetic, and was used medically for that purpose in the early part of the century. Procaine and xylocaine, synthetic local anesthetics introduced during the mid-1900s, have replaced cocaine as a medical drug.

Another pleasurable yet addictive drug is nicotine, usually obtained by either smoking or chewing leaves of the tobacco plant, Nicotiana tabacum. Ground-up leaves, known as snuff, may be placed in the nose or cheek, allowing the nicotine to diffuse through the linings of the cavities into the bloodstream.

With the possible exception of alcohol, nicotine is the world's most widely used addictive drug. Its attractiveness undoubtedly results from the drug's paradoxical combination of calming and stimulating properties—it can produce either relaxation or arousal, depending on the user's state. Its physical effects, however, are primarily stimulatory. By increasing the heart rate and blood pressure while constricting the arteries—including those in the heart—nicotine significantly increases the risk of a heart attack.

Some alkaloid stimulants are not addictive, however. These include caffeine and the related compounds theophylline and theobromine. Caffeine is found in coffee, made from beans of Coffea arabica; in tea, from leaves of Camellia sinensis; in cocoa and chocolate, from seeds of Theobroma cacao; and in cola drinks, which contain flavorings derived from nuts of Cola plants. In northern Argentina and southern Brazil, leaves of Ilex paraguariensis (a type of holly) are used to make maté, a drink more popular there than either coffee or tea.

In addition to caffeine, tea also contains small amounts of theophylline, while theobromine is the major stimulant in cocoa. Large amounts of coffee, tea, cocoa, or cola drinks (more than 6-12 cups of coffee a day, for example), can produce nervousness, shakiness (muscle tremors), and insomnia, and may increase the risk of heart attack. Adverse effects from smaller amounts of these beverages have been claimed but never clearly demonstrated.

Black pepper falls into an entirely different category of the pain/pleasure grouping. This spice derives its burning flavor primarily from the alkaloids piperine, piperidine, and chavicine.