Increased HIV and hepatitis B and C transmission are consequences of increased methamphetamine abuse, not only in individuals who inject the drug, but also in noninjecting methamphetamine abusers. Among injection drug users, infection with HIV and other infectious diseases is spread primarily through the re-use of contaminated syringes, needles, or other paraphernalia by more than one person. However, regardless of how it is taken, the intoxicating effects of methamphetamine can alter judgment and inhibition and lead people to engage in unsafe behaviors.

Methamphetamine has become associated with a culture of risky sexual behavior, both among men who have sex with men (MSM) and heterosexual populations. This link may be due to the fact that methamphetamine and related psychomotor stimulants can increase libido. Paradoxically, long-term methamphetamine abuse may be associated with decreased sexual functioning, at least in men. The combination of injection and sexual risk-taking may result in HIV becoming a greater problem among methamphetamine abusers than among opiate and other drug abusers, something that already seems to be occurring, according to some epidemiologic reports. For example, while the link between HIV infection and methamphetamine abuse has not yet been established for heterosexuals, data show an association between methamphetamine abuse and the spread of HIV among MSM.

Methamphetamine abuse may also worsen the progression of HIV and its consequences. In animal studies, methamphetamine increased viral replication; in human methamphetamine abusers, HIV caused greater neuronal injury and cognitive impairment compared with nondrug abusers.

NIDA-funded research has found that, through drug abuse treatment, prevention, and community-based outreach programs, drug abusers can change their HIV risk behaviors. Drug abuse can be eliminated and drug-related risk behaviors, such as needle-sharing and unsafe sexual practices, can be reduced significantly, thus decreasing the risk of exposure to HIV and other infectious diseases. Therefore, drug abuse treatment is HIV prevention.