Substance dependence

Substance dependence is a pattern of repeated use of alcohol or drugs that usually causes tolerance, withdrawal, and compulsive drug or alcohol use.

• Tolerance is the need for increased amounts of alcohol, drugs, or both to achieve the desired effect, or a decreased effect that results when using the same amount of alcohol or drugs. How rapidly tolerance develops depends on the substance and the pattern of abuse. People who use opioids, such as heroin, opium, or pain medications, and stimulants, such as cocaine and amphetamines, can rapidly develop a tolerance to a dose that would kill someone who does not use these drugs. Alcohol tolerance can also be very strong.
• Withdrawal is an uncomfortable physical or emotional change caused by decreased amounts of alcohol or drugs in the body of a heavy user. After experiencing unpleasant withdrawal symptoms, the user is likely to take an increased amount of alcohol or drugs to avoid more of these symptoms. Withdrawal symptoms occur with alcohol, heroin, pain medications, and sleeping pills but may not be as noticeable with stimulants such as amphetamines, cocaine, or nicotine.
• Compulsive use is the need for larger amounts of alcohol or drugs or failed attempts to control or cut down on these substances. A great deal of time is spent getting, using, and recovering from the alcohol or drug. The user cannot stop using the alcohol or drugs despite the undesired effects and difficulties they cause.

People with dependence frequently have a long history of intoxication and withdrawal alternating with attempts to remain drug- or alcohol-free. Dependence on a single substance may lead some people to use and develop a dependence on another substance. Alcohol dependence is particularly common in people already dependent on drugs, such as methamphetamines, opioids, or cocaine.