Amphetamines (am-FET-a-meens) are powerful stimulant drugs. Because of the intense high caused by amphetamines, they've become extremely popular street drugs. Some common street names include 'speed', 'crank', 'meth', and 'crystal'. They affect the brain and central nervous system by producing a powerful sense of euphoria, along with extreme alertness, increased energy, nervous excitement, irritability, and insomnia. This sense of euphoria is followed by a 'crash', caused by the exhaustion of the central nervous system, which in turn may cause panic, paranoia, and nervousness. Other effects of amphetamines include an accelerated heart rate, increased respiration rate, and elevated blood pressure. In addition, a user's pupils become dilated, and there's usually a decrease in appetite. It's not unusual for the casual user to experience dry mouth, dizziness, sweating, headache, blurred vision, sleeplessness, and anxiety. High doses can cause irregular heartbeats and severe tremors, and frequent users are subject to greatly increased chances of stroke or heart failure. Tolerance to the drug builds rapidly, and users require ever-increasing amounts to produce the desired effect. Chronic users often suffer from additional side effects, including increased aggression, fear, hallucinations, or seizures. For more information about amphetamines, consult a health care provider.