drug

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Any of a range of substances, natural or synthetic, administered to humans and animals as therapeutic agents: to diagnose, prevent, or treat disease, or to assist recovery from injury. Traditionally many drugs were obtained from plants or animals; some minerals also had medicinal value. Today, increasing numbers of drugs are synthesized in the laboratory. It is useful to categorize drugs used by humans into three groups: over-the-counter and prescription drugs (medicines) such as paracetamol and penicillin; recreational drugs such as alcohol and nicotine; and the drugs which are taken illegally if they are not prescribed, such as amphetamines, cannabis, and cocaine.

Drugs are administered in various ways, including orally, by injection, as a lotion or ointment, as a pessary, by inhalation, or by transdermal patch.

One of the first scientific investigations of the effect of a drug on the human body was of digitalis. Digitalis is a mixture of drugs from the foxglove (Digitalis purpurea). Its effect is to increase the force of contraction of heart muscle. It is still used to help treat a number of heart problems, such as heart failure.

Drugs prescribed by doctors may have unwanted side effects. Side effects are normally slight, but overdoses and mixing with other drugs can make the side effects worse. These effects can be dangerous. Paracetamol reduces pain, but in large doses it is poisonous and can kill.

Some drugs can become addictive (see addiction). The most commonly used addictive drug is nicotine. Regular smokers find that the addiction causes it to be very difficult or impossible to give up smoking even though they try. Even more dangerous than nicotine are some mind-affecting addictive drugs. The illegal drugs cocaine and crack are addictive and users find that they have to take more of the drug to get the same effect once they are addicted. Large doses of these drugs can kill.

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