CNS stimulants, or central nervous system stimulants, are substances that increase brain activity, leading to heightened alertness, attention, and energy levels. They work by enhancing the effects of certain neurotransmitters, such as dopamine and norepinephrine, which play key roles in mood and focus. Common examples include amphetamine, methylphenidate, and caffeine. These stimulants are often prescribed to treat conditions like Attention Deficit Hyperactivity Disorder (ADHD) and narcolepsy. While they can improve concentration and reduce fatigue, they may also lead to side effects such as increased heart rate, anxiety, and insomnia if misused or taken in high doses.