Placebos

Placebos are substances that are made to resemble drugs but do not contain an active drug.

A placebo is made to look exactly like a real drug but is made of an inactive substance such as a starch or sugar. Placebos are usually used in research studies.

Placebos can result in or be coincidentally associated with many changes, both desirable and undesirable. This phenomenon, called the placebo effect, appears to have two components: anticipation of results, usually optimistic, from taking a drug (sometimes called suggestibility); and spontaneous change. Sometimes people improve spontaneously, without treatment. If spontaneous change--whether positive or negative--occurs after a placebo is taken, the placebo may incorrectly be credited with or blamed for the result.

Some people seem more susceptible to the placebo effect than others. People who have a positive opinion of drugs, doctors, nurses, and hospitals are more likely to respond favorably to placebos than are people who have a negative opinion. Some people who are particularly susceptible to placebos tend to become compulsive about using the drug; they tend to increase the dose, and they develop withdrawal symptoms when they are deprived of the placebo.

When a new drug is being developed, investigators conduct studies to compare the effect of the drug with that of a placebo because any drug can have a placebo effect, unrelated to its action. The true drug effect must be distinguished from a placebo effect. Half the study's participants are given the drug, and half are given an identical-looking placebo. Ideally, neither the participants nor the investigators know who received the drug and who received the placebo (this type of study is called a double-blind study).

When the study is completed, all changes observed in participants taking the active drug are compared with those in participants taking the placebo. The drug must perform significantly better than the placebo to justify its use. In some studies, as many as 50% of participants taking the placebo improve (an example of the placebo effect), making it difficult to show the effectiveness of the drug being tested.

See the sidebar Placebo: I Shall Please.