Alcohol use is related to HIV/AIDS through two major venues: risky sexual behaviour and decreased immune system efficiency.

After drinking alcohol, impaired judgment and reduced inhibitions often cause people to forget or neglect to practice safe sex, or even engage in violent behaviour such as rape. Alcohol, especially in chronic consumption, can also delay normal immune responses that protect the body from disease, which increases the drinker’s vulnerability to HIV when exposed to the virus, and can speed up the onset of AIDS-related illnesses in previously infected drinkers.

Although direct HIV spread in drug users is limited to injected drugs, other drugs such as ecstasy or marijuana can have a behavioural effect similar to alcohol. Using these drugs may lead to clouded judgment and rash decisions, which increases the likelihood of risky sexual behaviour.