Repeated use of meth can cause violent behavior, mood swings, and psychosis. Psychosis can include paranoia, hearing sounds that aren’t there, and delusions (e.g., the sensation of insects creeping on the skin). The paranoia can result in homicidal and suicidal thoughts.
Meth 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 meth use may be associated with decreased sexual function, at least in men.
Over time, meth use may also cause:
- Skin sores: Meth can make users feel like bugs are crawling on or under their skin (“crank bugs”), making them scratch a lot and causing sores on the face and arms.
- Severe weight loss: Meth users burn a lot of energy and don't eat well, which can make them lose a lot of weight and look sick.
- “Meth mouth”: Meth users' teeth become broken, stained, and rotten. Meth users often drink lots of sweet things, grind their teeth, and have dry mouths.
- Aging: Because of the weight loss, skin problems, and tooth problems, people who use meth start looking a lot older than they really are. Their hands or body might shake. Their skin looks dull and has sores and pimples that don't heal. Their mouth looks sunken as their teeth go bad.
- Problems with thinking, emotion, and memory: Meth changes brain circuits needed for learning and remembering things, and it can alter a person’s emotions and how they see the world. For instance, a person who is using meth might feel, hear, or see things that aren't there. They might think that people are out to get them, or start believing strange ideas that can't really be true. These effects can last for a long time even after a person quits using the drug.