What stimulants are you referring to? The prescription amphetamines? Well, Adderall can sometimes produce more paranoia compared to Dexedrine due to its contents of l-amphetamine. Methamphetamine can also cause paranoia due to its long duration, ROA and the large doses that are used to get high. Generally amphetamines increase focus/attention span and calm down hyperactivity. Although if you don't have ADHD, abusing them may have the opposite effect.