A face full of bleeding sores. Rotting and missing teeth. A thin face and nervous, edgy demeanor.

These are signs of methamphetamine addiction.

Methamphetamine, or "meth" is a central nervous system stimulant. It causes sleeplessness, suppresses the appetite, increases physical activity, causes rapid breathing and a fast, sometimes irregular, heartbeat. it can hike blood pressure, and make users feel excessively warm.

Long-term users are skinny, with blackened, rotting teeth, a condition called "meth mouth." The drug causes the salivary glands to dry out, which allows acids in the mouth to dissolve tooth enamel. Coupled with the meth users' constant teeth-grinding, tendency to eat little but sweets and soda, and neglect of hygiene, leads to tooth loss and serious decay.

Long-term meth users are anxious, moody and often prone to violent outbursts. Chronic meth users can also suffer from hallucinations and delusions, such as the sensation of bugs crawling under their skin. The bleeding sores seen on many meth users are from scratching the "meth bugs" they believe are under their skin, according to the National Institute on Drug Abuse.