THE EFFECTS OF DRUGS CHANGE OVER TIME

THE EFFECTS OF DRUGS CHANGE OVER TIME

When people recall the first time they drank alcohol, most remember that they got drunker than they would now if they drank the same amount. This isn't all just fading memory. Many drugs cause much smaller reac­tions in the body when someone uses the same drug regularly. This change is called tolerance. Usually the lesser reaction is due to previous

experience with that drug or a similar drug, but even intense stress might change the reactions to some drugs.

Think about all the drugs we take that keep working even with many doses: our morning cup of coffee, an occasional aspirin for a headache (imagine how much aspirin we all take over a lifetime!), an antacid to calm the stomach after a spicy meal. Why do these drugs keep working? The reason is that we usually take them only for a short time, or intermit­tently. The more frequently we take the drug, and the higher the dose, the more likely it is that tolerance will develop. So, with just one aspirin once

a week or even once a day, the body has plenty of time between doses to return to normal. Caffeine continues to provide that pleasant arousing effect that peo­ple associate with their morning cup of coffee or tea for years. However, bodies do adapt to the daily cup of coffee (see the "Caffeine" chapter), so that people who are regular coffee drinkers have smaller effects from (show tolerance to) caffeine compared to someone who never ingests it. So, tolerance builds up, but the normal daily dose is not enough lo cause the effect to go away entirely.

Tolerance to some drugs can be dramatic. For example, heroin addicts rapidly build up tolerance to opiate drugs. Longtime heroin addicts will take doses that would have killed them the first time they used the drug. This tolerance can last as long as several weeks or months. Tolerance lasts this long because addicts typically take many doses a day, every day, some­times for years, and some of the body's changes are very long-lasting.

What about antibiotics? Everyone probably remembers being exhorted to be sure to take every one of the two weeks' worth of pills, and tried (and perhaps failed) to be careful to take a dose every six to eight hours. Although no one bacterium adapts to the drug, the population as a whole often does adapt. Bacteria replicate between one and many times a day, so new generations are constantly appearing. When an individual bacte­rium appears that happens to be resistant to the drug, this individual and its offspring survive, and the infection becomes resistant. With the rising use of antibiotics (antibiotics in beef^-, antibiotics for many child­hood diseases, etc.), more and more humans are carrying resistant popu­lations of bacteria in their body that are difficult to treat with currently available antibiotics. This is drug tolerance playing out at the population level rather than the individual level, and it is becoming more of a prob‑

lem worldwide.

Some drugs actually become more effective over time. Cocaine is an example. Some of its effects become greater with each passing dose. 'Mere could be a beneficial side to this effect: drugs that gradually become more active could be delivered only occasionally and still be effective. This cer­tainly would be cheaper! Some researchers have proposed that antide­pressant drugs fit into this category, and that daily treatment may not be

necessary.

Fortunately, many of the drugs we rely on to treat disease are given in doses that do not cause the development of tolerance, so they can con­tinue working over a long period of time. This is especially important for drugs that are used to treat diseases like high blood pressure, which are lifelong conditions that require therapy for years.