When cannabis is combined with other drugs, such as alcohol, the effects can be greater than when one drug is taken by itself. Some cannabis users have lapsed into psychotic or near psychotic states after using cannabis particularly in heavy doses or for an extended time. Nevertheless it is recommended that people with a family history of schizophrenia or other psychosis avoid using cannabis. The behaviour becomes a major priority in the person's life to the exclusion of other behaviours. Drug dependence is one such addiction, of which the most familiar is chronic tobacco use.
Some drugs can produce a physical dependency when the body adapts to the presence of the drug.
If the user stops taking the drug they may experience withdrawal symptoms as the body readjusts to functioning without it. People with physical dependence will develop tolerance and need more of the drug to gain the same effect. Withdrawal syndromes differ for various drugs. They may include irritability, nausea, sleeplessness, anxiety, vomiting, stomach cramps and last for a week or more until the drug is metabolised totally or eliminated from the body. Medication may be used to assist some withdrawal syndromes.