If someone uses amphetamine regularly or takes a high dose they are likely to feel anxious, irritable and sometimes paranoid. Large doses of amphetamine are known to cause amphetamine psychosis. This is clinically very similar to other psychoses - like paranoid schizophrenia. People suffering from amphetamine psychosis often feel that there's a conspiracy, people are out to get them, they've done something wrong and that everyone else knows all about it. This can be extremely frightening, but will usually wear off as the speed wears off.
Amphetamines stimulate the central nervous system.
Common reactions include dilated pupils, dry mouth, loss of appetite, an increase in body ntemperature and imsomnia. Higher doses can cause stomach upset, sweating, jaw tension, a disturbed heart rythm, flushing and cold hands and feet. Less common are increased blood pressure, palpitations and tremors. Regular use of amphetamines will interrupt sleep patterns and eating habits, and can lead to extreme paranoid delusions. Someone who feels upset or anxious who uses speed will find that their feelings are intensified as they come down from the effects of the drug.