Stimulants are drugs that increase alertness, energy, and bodily functions by stimulating the brain and nervous system. They have been used medically to treat conditions like narcolepsy and ADHD. However, stimulants can also be abused recreationally and lead to addiction. Common stimulants include caffeine, cocaine, amphetamines, and ingredients in energy drinks. While stimulants provide short-term effects like increased energy, they can cause serious long-term health problems if abused, such as heart disease, organ damage, and psychological issues.