Stimulants are a class of drugs that increase the activity of the central nervous system and can cause changes in mood, behaviour, and cognitive function. Common effects can include alertness, wakefulness, and energy, as well as increased heart rate and blood pressure. Some stimulants can cause euphoria, increased sociability, and enhanced cognitive performance. They can treat conditions such as attention deficit hyperactivity disorder (ADHD) and narcolepsy. Examples of stimulants include: amphetamines (Adderall and Ritalin), methylphenidate (e.g. Ritalin and Concerta), cocaine, caffeine, and nicotine.