Crystal methamphetamine is a central nervous system stimulant. It is crystalline and white or nearly clear in color. It's usually snorted, but it's also commonly smoked and less commonly injected or consumed orally.
Meth is extremely addictive and more powerful than any other speed, making it very seductive to anyone already fond of other forms of stimulants. Methamphetamine creates a rush by flooding the brain with dopamine, a neurotransmitter that plays a role in bodily movement, emotions and the feeling of pleasure and pain. The increase in dopamine caused by methamphetamine isn't naturally duplicable. In order to feel that sensation again, a user has to use meth again. Over time, as with any addictive substance, the effects of the drug lessen as the user's tolerance grows, requiring more and more of the drug to reach similar highs.
Long-term use affects the brain's very ability to produce or use dopamine naturally. Meth addicts (as well as those addicted to most drugs) generally have lower levels of dopamine receptors than nonaddicts. Because of this deficiency, the ability to feel pleasure is diminished for a newly sober addict breaking free from crystal meth. The onset of depression and hopelessness caused by low levels of dopamine lead many addicts right back to the drug, as it provides -- in the short term -- the best opportunity to feel anything close to normal again. In time, the brain's natural dopamine capabilities return to pre-addiction levels, but the length of time it takes varies.
Taking meth makes the user more alert. The heart races, breathing quickens and sweat glands kick into overdrive. Users may become extremely talkative or withdraw into a private sphere of self-interest. They often feel superhuman, empowered, more intelligent and more perceptive.
Users can also maintain their interest in mundane activities for great lengths of time. As a result, performance of repetitive tasks continues at a high level for hours and hours, when normally it might wane due to boredom. Assembly-line workers and others who perform the same physical motion over and over suddenly find their work to be invigorating and even fascinating when on crystal meth. Where life once seemed dreary and methodical, meth users may find that the drug keeps them "tuned in" to their work, speeding up their thoughts as well as their perception of the passing of time.
Appetite is nearly nonexistent for someone on meth. This may make the drug seem tempting to a person trying to lose weight, but weight won't be the only thing that person loses. Over time, teeth decay, crack and fall out of the skull, a condition known as "meth mouth." Lesions can form on the skin from excessive scratching.
Extended use of this stimulant can make people feel as if they've lost their minds. After days of staying awake, strange images dart in and out of the corners of the visual field, nonexistent sounds come from near and far, and the user's laser focus zeroes in on perceived threats or injustices. In short, you wouldn't want to spend a week in a foxhole with a Nazi who's eating the stuff like it's candy. Which is exactly what Nazis did in World War II, something we'll discuss in the next section.