Some allergic reactions are mediated by an endogenous substance called histamine that strongly affects nerves, blood vessels, and other tissues. In an effort to suppress allergic symptoms, pharmacologists have invented a number of synthetic drugs to block the actions of histamine. Many antihistamines are now available; in large-dosage forms they are dispensed by prescription, but lower-dosage forms are sold over the counter. Some of the ones in widespread use are: diphenhydramine (Benadryl), chlorpheniramine (Teldrin, Chlor-Trimeton), brompheniramine (Dimetane), dexchlorpheniramine (Polaramine), tripelennamine (PBZ, Pyri-benzamine), tripolidine (Actidil), promethazine (Phenergan), pyril-amine, and doxylamine.
Although antihistamines are strong drugs that affect many systems of the body, they are often not very efficient at doing what they are supposed to do: counteract histamine and suppress allergies. The central nervous system is especially sensitive to antihistamines. Often these drugs cause profound alterations of mood, not for the better. They make people depressed, grouchy, lethargic, drowsy, and unable to think clearly. Some of them are related chemically to major tranquilizers like Thorazine, which produce similar effects on mood. The sedation caused by antihistamines are likely to interfere with driving and other activities requiring concentration, clear thinking, and good reflexes. These effects are intensified by the simultaneous use of alcohol and other depressants. Recently, new antihistamines have appeared that do not enter the brain. The best known of these is terfenadine (Seldane). It does not cause sedation and depression but often causes headaches and other uncomfortable side effects. It is much more expensive than older antihistamines.
Despite their tendency to put people in bad moods, antihistamines are among the most widely consumed of all medical drugs, and neither doctors nor patients think of them as psychoactive. Furthermore, antihistamines are common ingredients of many over-the-counter preparations, such as cold remedies and sleeping aids; they sometimes even arrive in the mail in free samples of these products. Anyone suffering from chronic depression and lethargy should make sure they are not consuming these chemicals in one form or another. Allergy sufferers should also know that allergic symptoms frequently respond to nondrug treatments, such as changes in diet and mental state, making it possible to avoid antihistamines entirely.
A few drugs in this class are used specifically to prevent motion sickness. Dimenhydrinate (Dramamine) is the best known. Like its relatives, it often makes people drowsy and puts them in unwelcome states of mind.
Oddly enough, one antihistamine is used by some people, mostly junkies, to get high. It is tripelennamine, sold under the brand names PBZ and Pyribenzamine. Because a common form of it is a blue tablet, it is known as "blues" on the street. The combination of morphine and blues is called "blue velvet"; some junkies like to inject it intravenously. A more popular combination is the synthetic opiate pentazocine (Talwin) and PBZ, wrhich is known as "T's and B's" or "T's and blues" and is also taken intravenously. Except for this strange practice, recreational use of antihistamines is rare to nonexistent.
The use of antihistamines in high doses or over long periods seems unwise. These drugs have known toxicity on the physical body, and no one should spend more time than necessary in the mental states they produce.
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