Ritalin is used to treat Attention Deficit Disorder (ADD), which is also known as Attention Deficit/Hyperactivity Disorder (ADHD). When taken according to usual prescription instructions it has a calming effect and can help the person focus. Since Ritalin is a stimulant and works on the neurotransmitter dopamine, when taken unprescribed it can lead to a strong stimulant effect similar to cocaine.
Some negative consequences associated with using Ritalin include the following:
nervousness and insomnia;
loss of appetite;
tremors, convulsions, and headaches;
irregular heartbeat and respirations;
anxiety, depression, and restlessness;
paranoia, hallucinations, and delusions;
excessive repetition of movements and meaningless tasks; and
formicaton (sensation of bugs or worms crawling under the skin).