Stimulant drugs are substances that increase activity in the central nervous system, leading to heightened alertness, energy, and attention. Common examples include caffeine, nicotine, and prescription medications like amphetamine and methylphenidate. These drugs can enhance mood and cognitive function but may also lead to side effects such as increased heart rate and anxiety. While some stimulants are used medically to treat conditions like ADHD and narcolepsy, others are misused for recreational purposes. Prolonged use can result in dependence and withdrawal symptoms. It's important to use stimulant drugs responsibly and under medical supervision when necessary.