DRUGS
Most people in the Western world consume drugs of one sort or another throughout their lives. Drugs, however. have usually been designed to be highly potent in biological sys- tems and consequently many are potentially toxic. Drug toxicity may be due either to an overdose or it may be a rare and unusual adverse effect, and examples of both of these will be considered in detail in Chapter 5. Drugs vary enormously in chemical structure and possess a wide variety of biological activ- ities. They are probably the only foreign sub- stances of known biological activity that man ingests intentionally. Included in this category are alcohol and the active principles in cigar ettes, both of which are used because of their of course, have biological activity and both, toxic properties. Drugs used in veterinary prac- tice must also be considered here (and in the next section) as humans may consume meat from or other food derived from animals treated with these drugs.