As with many other drugs of abuse, repeated stimulant abuse can cause addiction. That means that someone repeatedly seeks out and uses the drug despite its harmful effects. Repeated drug use changes the brain in ways that contribute to the drug craving and continued drug seeking and use that characterizes addiction. Other effects of long-term stimulant abuse can include paranoia, aggressiveness, extreme anorexia, thinking problems, visual and auditory hallucinations, delusions, and severe dental problems.
Repeated use of cocaine can lead to tolerance of its euphoric effects, causing the person to take greater amounts or to use the drug more frequently (e.g., binge use) to get the same effects. Such use can lead to bizarre, erratic behavior. Some people who abuse cocaine experience panic attacks or episodes of full-blown paranoid psychosis, in which the individual loses touch with reality and hears sounds that aren’t there (auditory hallucinations). Different ways of using cocaine can produce different adverse effects. For example, regularly snorting cocaine can lead to hoarseness, loss of the sense of smell, nosebleeds, and a chronically runny nose. Cocaine taken orally can cause reduced blood flow, leading to bowel problems.
Repeated use of methamphetamine can cause violent behavior, mood disturbances, and psychosis, which can include paranoia, auditory hallucinations, and delusions (e.g., the sensation of insects creeping on the skin, called “formication”). The paranoia can result in homicidal and suicidal thoughts. Methamphetamine can increase a person’s sex drive and is linked to risky sexual behaviors and the transmission of infectious diseases, such as HIV. However, research also indicates that long-term methamphetamine use may be associated with decreased sexual function, at least in men.