Pulmonary complications, including various types of pneumonia, may also result from the unhealthy lifestyle of the user, as well as from the depressant effect of opiates on respiration. This means the user must use more of the drug to achieve the same intensity of effect. Chronic users may also become psychologically and physically dependent on opioids. Psychological dependence exists when a drug is so central to a person's thoughts, emotions, and activities that the need to continue its use becomes a craving or compulsion. With physical dependence, the body has adapted to the presence of the drug, and withdrawal symptoms occur if use of the drug is reduced or stopped abruptly.
Some users take heroin on an occasional basis, thus avoiding physical dependence.
Withdrawal from opioids, which in regular users may occur as early as a few hours after the last administration, produces uneasiness, yawning, tears, diarrhea, abdominal cramps, goose bumps, and runny nose. These symptoms are accompanied by a craving for the drug. Major withdrawal symptoms peak between 48 and 72 hours after the last dose and subside after a week. Some bodily functions, however, do not return to normal levels for as long as six months. Sudden withdrawal by heavily dependent users who are in poor health has occasionally been fatal.