Stimulants are drugs that increase your heart rate, breathing rate, and brain function. Some stimulants affect only a specific organ, such as the heart, lungs, brain, or nervous system.

Epinephrine is a stimulant. It is given during cardiac arrest to make the heart beat.

Other times, stimulants can cause unwanted side effects. For example, pseudoephedrine found in some cold medicines can increase the heart rate.