Reduced blood flow in prefrontal cortex of<unk>  users.<unk>  use is associated with comorbid mental health problems, such as mood and anxiety disorders, and discontinuing<unk>  use is difficult for some users. Psychiatric comorbidities are often present in dependent<unk>  users including a range of personality disorders. Based on annual survey data, some high school seniors who report smoking daily (nearly 7%, according to one study) may function at a lower rate in school than students that do not. The sedating and anxiolytic properties of tetrahydrocannabinol (THC) in some users might make the use of<unk>  an attempt to self-medicate personality or psychiatric disorders. Dependency Prolonged<unk>  use produces both pharmacokinetic changes (how the drug is absorbed, distributed, metabolized, and excreted) and pharmacodynamic changes (how the drug interacts with target cells) to the body. These changes require the user to consume higher doses of the drug to achieve a common desirable effect (known as a higher tolerance), reinforcing the body's metabolic systems for eliminating the drug more efficiently and further down-regulating<unk> oid receptors in the brain.<unk>  users have shown decreased reactivity to dopamine, suggesting a possible link to a dampening of the reward system of the brain and an increase in negative emotion and addiction severity.<unk>  users can develop tolerance to the effects of THC. Tolerance to the behavioral and psychological effects of THC has been demonstrated in adolescent humans and animals. The mechanisms that create this tolerance to THC are thought to involve changes in<unk> oid receptor function. One study has shown that between 2001–2002 and 2012–2013, the use of marijuana in the US doubled.<unk>  dependence develops in about 9% of users, significantly less than that of heroin, cocaine, alcohol, and prescribed anxiolytics, but slightly higher than that for psilocybin, mescaline, or LSD. Of those who use<unk>  daily, 10–20% develop dependence. Withdrawal<unk>  withdrawal symptoms occur in one-half of people in treatment for<unk> s. Symptoms may include dysphoria (anxiety, irritability, depression, restlessness), disturbed sleep, gastrointestinal symptoms, and decreased appetite. It is often paired with rhythmic movement disorder. Most symptoms begin during the first week of abstinence and resolve after a few weeks. About 12% of heavy<unk>  users showed<unk>  withdrawal as defined by the DSM-5, and this was associated with significant disability as well as mood, anxiety and personality disorders.
Cannabis use disorder
Benzodiazepine use disorder
Stimulant use disorder
Opioid use disorder
Amphetamine dependence
Benzodiazepine dependence
Polysubstance dependence
Substance dependence