There are a few ways a person can take drugs, including injection, inhalation and ingestion. The effects of the drug on the body can depend on how the drug is delivered. For example, the injection of drugs directly into the bloodstream has an immediate impact, while ingestion has a delayed effect. But all misused drugs affect the brain. They cause large amounts of dopamine, a neurotransmitter that helps regulate our emotions, motivation and feelings of pleasure, to flood the brain and produce a “high.” Eventually, drugs can change how the brain works and interfere with a person’s ability to make choices, leading to intense cravings and compulsive drug use. Over time, this behavior can turn into a substance dependency, or drug addiction.
^ Jump up to: a b "Substance use disorder". Pubmed Health. National Institutes of Health. Archived from the original on 31 March 2014. Retrieved 12 September 2014. Drug dependence means that a person needs a drug to function normally. Abruptly stopping the drug leads to withdrawal symptoms. Drug addiction is the compulsive use of a substance, despite its negative or dangerous effects Drug and Alcohol Treatment Centers ► The Problem With Relapse
Stimulants, such as tobacco, cocaine or prescription amphetamines, stimulate the brain and nervous system, causing increased alertness. Depressants, such as barbiturates and benzodiazepines, slow activity in the brain and nervous system, causing relaxation. Hallucinogens, such as LSD and PCP, drastically disrupt the way the brain and nervous system communicate, causing hallucinations. Rehab: Last Week Tonight with John Oliver (HBO)