Drug Dependence In order for a chemical to be considered a drug it must have the capacity toaffect how the body works–to be biologically active. No substance that has thepower to do this is completely safe, and drugs are approved only after theydemonstrate that they are relatively safe when used as directed, and when thebenefits outweigh their risks. Thus, some very dangerous drugs are approvedbecause they are necessary to treat serious illness.
Digitalis, which causes theheart muscle to contract, is a dangerous drug, but doctors are permitted to useit because it is vital for treating patients whose heart muscle is weak. A drugas potent as digitalis would not be approved to treat such minor ailments astemporary fatigue because the risks outweigh the benefits. Many persons suffer ill effects from drugs even though they take the drugexactly as directed by the doctor or the label. The human population, unlike acolony of ants or bees, contains a great variety of genetic variation. Drugs aretested on at most a few thousand people.
When that same drug is taken bymillions, some people may not respond in a predictable way to the drug. A personwho has a so-called idiosyncratic response to a particular sedative, for example,may become excited rather than relaxed. Others may be hypersensitive, orextremely sensitive, to certain drugs, suffering reactions that resembleallergies. A patient may also acquire a tolerance for a certain drug.
This means thatever-larger doses are necessary to produce the desired therapeutic effect. Tolerance may lead to habituation, in which the person becomes so dependent uponthe drug that he or she becomes addicted to it. Addiction causes severepsychological and physical disturbances when the drug is taken away. Morphine,cocaine, and Benzedrine are common habit-forming drugs.
Finally, drugs oftenhave unwanted side effects. These usually cause only minor discomfort such as askin rash, headache, or drowsiness. Certain drugs, however, can produce serious,even life-threatening adverse reactions. For example, the drug Thalidomide wasonce called one of the safest sedatives ever developed, but thousands of womenin the United Kingdom who took it during pregnancy gave birth to seriouslydeformed babies. Other adverse reactions stem from mixing drugs. Thus, takingaspirin, which has blood-thinning qualities, for a headache can be very harmfulif one is also taking other blood-thinning drugs such as heparin or dicumarol.
