This means that larger doses are needed to get an effect. This can happen with many different drugs. Drugs can change the chemistry of the body and physical dependency results from the repeated heavy use of drugs like heroin, tranquillisers and alcohol. If someone does not get a repeat dose they suffer physical withdrawal symptoms. They have to keep taking the drugs to stop themselves from feeling ill.
Psychological dependency is more common and can occur with any drug.
They feel that they cannot cope without drugs even though they may not be physically dependent. When a person's whole life is devoted to buying and taking drugs, you can say that the person is addicted to drugs. This usually applies to those who are regular, heavy users of drugs such as heroin and cocaine. These are the unpleasant symptoms which can result from stopping long-term use of certain drugs like alcohol, heroin and tranquillisers.