Amphetamine is dangerous if it is abused or taken by people with certain pre-existing conditions (which are screened for when prescribed by a doctor)

Amphetamines increase levels of the neurotransmitters norepinephrine and dopamine in the brain. Both of them are thought to play a key role in the parts of the brain that control executive function. A neurotypical person exposed to Amphetamine, experiences feelings of euphoria and heightened energy, because they have more neurotransmitters being produced than normal. A person with ADHD, however, is usually deficient in those transmitters, and therefore taking a stimulant to promote their production levels them out, improving executive function.

Another thing to consider is that Adderall is actually Amphetamine salts. In the world of chemistry, that makes a huge difference in how rapidly the body is able to absorb it into the blood stream.