An addict is a person who has an uncontrollable compulsion to repeat a behavior regardless of its negative consequence. There are many drugs that can lead to a condition recognized as addiction. The common symptoms are a craving for more of the drug, increased psychological tolerance to exposure, and withdrawal symptoms in the absence of the stimulus. A risk of dependency exists in most drugs that directly provide pleasure or relief.

There are two types of dependency - physical and psychological. Physical dependency on a substance is defined by the appearance of characteristic withdrawal symptoms when the drug is suddenly discontinued. Opioids, benzodiazepines, barbiturates, alcohol and nicotine are well known addictive drugs known for their ability to induce physical dependence. Cortisone, beta-blockers and most antidepressants are examples of similar such drugs, but they are not addictive. Some highly addictive drugs, such as cocaine, induce little physical dependence too. The main characteristic of an addictive drug is its ability to induce euphoria while causing harm.

The dependency of the mind leads to psychological withdrawal symptoms. Eating disorders are sometimes considered as psychological disorders and are sometimes treated as addictions. Withdrawal symptoms faced when the diet is altered suggests that food substances like chocolate, caffeine and sugar have the potential for addiction. Nicotine is considered to be the most addictive substance in the world.

Anxiolytics are used to reduce the symptoms of withdrawal in people with chemical dependency. In chronic opiate addiction, a surrogate drug such as methadone is offered. There are various models to treat dependency like the opponent-process model, the disease model, the genetic model, the cultural model, and the blended model. The term addiction is sometimes used loosely rather than as a medical classification. Endorphins are released as a result of pleasurable activity. This endorphin rush can become addictive. Opioids pose extreme risk of dependency because they are chemically similar to endorphins. Cocaine and amphetamines also pose risks associated with physical attenuation by increasing the levels of the neurotransmitters dopamine and norepinephrine, which acts indirectly to stimulate dopaminergic pathways in the brain.

Craving is the incredible desire an addict or alcoholic still feels for the substance. It takes often days, months or even years for recovery. It could be directly related to the long term changes in brain functioning. Relapse triggers can create powerful emotional and physical responses that can lead up to incredible urges to use drugs and alcohol again. It may result in the addict feeling angry, lonely, depressed or in self pity. Thus it becomes essential for individuals early into drugs to change their habit and different aspects of life.