There appears to be several words relating to this concept. One is Morgellon's Disease, a physical condition though its classification as a new illness is debateable.

Most doctors, including dermatologists and psychiatrists, regard Morgellons as a manifestation of known medical conditions, including delusional parasitosis The second, as mentioned in the above quote, is delusional parasitosis, which is a form of psychosis that results in the belief of crawling on / beneath the skin. However this sensation isn't always related to psychosis of course; the feeling itself is refered to as formication.

An amine derivative of amphetamine, C10H15N, used in the form of its crystalline hydrochloride as a central nervous system stimulant, both medically and illicitly. "Meth" is a stimulate drug that is used to let people go faster than they are normally supposed to. This drug basically speeds up your heart rate and lets you stay awake for inhuman - like periods of time. [I've edited a specific section on this answer due to the WikiAnswers Plagiarism Policy.] [I've edited out dead links and added the working addresses to the "links" section of the question.] Opinion One It doesn't matter what it is! It's illegal and can kill you so don't use it! SCARY STUFF MAN. (Never taken it, but drugs scare me)

Drug Name:

Metamphetamines

Drug Type:

Stimulant

Facts for Parents:

Some users avoid sleep 3 to 15 days.

Other Names:

Speed, meth, crank, crystal, ice, fire, croak, crypto, white cross, glass. "Ice" is the street name for the smokeable form.

How Consumed:

Orally, injected, snorted, or smoked

Effects:

Addiction, irritability, aggression, hypothermia, stroke, paranoia, psychosis, convulsions, heart and blood vessel toxicity, hallucinations, arrhythmia, formication (the sensation of insects creeping on or under your skin).

Meth is a synthetic drug that when taken effects the central nervous system. It contains toxic ingredients such as drain cleaner and lye.