Methamphetamine causes users to go from having healthy teeth to monstrostities for mouths like the one on the right. Tooth loss can occur within a year. The condition has been coined "meth mouth". The tooth decay of meth mouth is caused by meth's dry-mouth effect and the way the drug causes cravings for pop, teeth grinding and clenching, and long periods of poor oral hygiene. You can see more of thearticle at Science Daily.
Wow. I think a lot fewer people would try meth if you showed them this picture.