Unlike medicines, they have not been tested to make sure they are safe. Drugs of abuse are often illegal and some are extremely dangerous. Some drugs cause damage, for example to the brain or the liver. Many drugs are addictive and so the user can't give them up easily. The problems facing smokers Caffeine and alcohol can be misused, though in small amounts they are not thought to cause health problems.
Smoking is a very addictive type of drug abuse.
Tar and other dangerous chemicals in cigarette smoke cause many serious health problems. Illegal drugs Cocaine, heroin and cannabis are examples of illegal drugs. One of the problems with these is that drug users may move on from one type of drug to another. They might become addicted and then get involved in crime to pay for their habit.