At times, the allergy isn’t to a drug itself but to one of various additives. Artificial colors and flavorings are routinely added to drug compounds to make them both more palatable for consumers to swallow and easier for doctors, nurses and pharmacists to identify. Preservatives, fillers and coatings all show up.

And an additive in a drug is just likely to cause allergy as one in a food. For example, in his book Why Childs Is Hyperactive (Random House, 1975) Benjamin Feingold, M.D., tells of two young women taking birth control pills who developed wheezing and coughing, watery eyes and labored breathing.

They are afraid they’d developed asthma. As it turned out, however, they were simply allergic to artificial coloring in the birth control pills (incidentally, the hormones themselves can cause allergy like symptoms – stuffy nose, itching, hives – even asthma). Many antihistamines, antihistamine decongestants, corticosteroids, bronchodilators and theophylline (a muscle relaxer), among others, often contain they yellow dye tartrazine.

Ironically, those drugs are the mainstay of medical treatment of asthma and respiratory allergy. Since 1980, however, pharmaceutical manufacturers in the United States have been required to list tartrazine (also listed as FD&C Yellow No. 5) on drug labels, so you and your doctor can avoid the problem.

A capsule or tablet can also contain non-chemical additives you could be allergic to – for instance, starch derived from corn, potato, sorghum or other food. Or medications can have a binder made from pork, beef or lamb fat, a potential problem for anyone allergic to those meats.

Allergies to Illegal Drugs

Most people take drugs that are either or brought over the counter in a supermarket or pharmacy. Some drugs, however, are bought on the street – they're illegal. Aside from ruining health, abused drugs produce their share of allergic reactions. Barbiturates can trigger not only rashes but overall shedding of the skin, and can also raise large blister around the mouth and at pressure points such as attacks. Cocaine, too, can cause serious asthma.

Marijuana harbors some of the very molds that trigger allergy in asthmatics if that’s not bad enough, smoking marijuana releases some of the same nasty chemicals (such as benzopyrene and hydrocarbons) as regular cigarettes, making marijuana as abrasive to an asthmatic’s lungs as tobacco. Even if a person doesn’t have asthma, marijuana can cause red, hypoglycemia, muscular in coordination, nausea, respiratory depression, spasms and urinary frequency.

Will You React?

Although no one knows the exact why one person develops sensitivity to a drug and another doesn’t, certain recognized factors may alter your vulnerability.

Nature of the drug. Some drugs, such as milk of magnesia, rarely cause allergic reactions. Others – namely penicillin, aspirin compounds and the sulfonamides – account for 80 to 90 percent of all allergic drug reactions. Whether or not a drug will cause allergy seems to depend on it's ability (or the ability of one of it's byproducts) to latch onto a protein.

And once you’ve had an allergic response to one drug, you’re open to cross reactions to chemically similar drugs. Remember, aspirin cross reacts with other analgesics or the food coloring tartrazine. So anyone who reacted to one drug is likely to react to new drugs.

How old you are. Children don't react to drugs as often as adults do, possibly because they use less.

Other allergies. Some evidence suggest that people with allergic disease (hay fever, eczema, asthma and the like) tend to react more readily to drugs. Other evidence says they don't. Nerveless, when allergic people do react to drugs, they seem to react more seriously. For instance, an allergic person is three to ten times more likely to suffer an anaphylactic reaction to a drug than a non-allergic person.

Other conditions. Doctors says that the risk of reacting is greater among people with a chronic illness. But, they say, that’s probably not because the people are sick but because they take a lot of drugs.

How the drugs is taken. Perhaps because the skin is such a sensitive organ, drugs applied topically are more prone to cause reactions than those you swallow. Because of that increased risk, certain drugs, such as penicillin and sulfonamides, are no longer used in salves.

Along the same line, you may react to an oral drug if you previously reacted to the drug when it was applied to your skin. For instance, if you once reacted to mercury containing methiolate painted on a scratch or cut, you could eventually react to a mercury containing diuretic. An injection drug, however, is more likely to cause in immediate and severe reaction, since it enters the system quickly.