The drugs are normally prescribed to treat attention deficit hyperactivity disorder (ADHD), but healthy students use them to get a leg up in school, by improving focus, concentration and memory.
Adrenaline, or epinephrine, is a hormone that dilates an individual's air passages and increases his heart rate when he is faced with a stressful situation. The hormone is secreted from the adrenal glands to help ensure survival under dangerous situations.
For example, the heart beats faster due to adrenaline. In order for adrenaline to be able to do this various organs have receptors (known as beta receptors) to accept the adrenaline and use it to behave differently in times of stress. Beta blockers block these receptors. They stop various organs in the body (depending on the beta blocker used) from accepting adrenaline.