In the short term, stimulants can produce feelings of tremendous joy, increased wakefulness, and decreased appetite. People who abuse them can become more talkative, energetic, or anxious and irritable. Other short-term effects of stimulants can include increased body temperature, heart rate, and blood pressure; dilated pupils; nausea; blurred vision; muscle spasms; and confusion.
Stimulants can also cause the body’s blood vessels to narrow, constricting the flow of blood, which forces the heart to work harder to pump blood through the body. The heart may work so hard that it temporarily loses its natural rhythm. This is called fibrillation and can be very dangerous because it stops the flow of blood through the body.