Methylphenidate is a stimulant medication. It works by stimulating the central nervous system, promoting focus, motivation, and creativity. It does this by sitmulating (activating) neurotransmitters (such as serotonin, known for promoting a heightened mood; and dopamine, known for promoting movement, and concetration) and releasing these certain chemicals for as long as the drug is broken down by the body. This drug is responsible for replacing the certain substances not originally produced by the brain (absence of these chemicals is what ADHD/ADD is comprised of; a deficiency of the appropriate chemicals to function properly and in an orderly fashion rather than erratically and all at the same time). However, this drug can also increase libido, causing an interest in sexual activity stronger than it would be without the drug. So, in short, stimulants make you more aroused. If you use them for a very long time in very high doses (depending on the susceptibility of the person to the drug), and then don't use as often or as much, your libido plummets. But, after time heals the brain from such damage to the neurotransmitters, libido returns back to normal levels. (This is my own research I've done on the drug.)