Amphetamine psychosis

# Overview
Amphetamine psychosis is a form of psychosis which can result from amphetamine or methamphetamine use. Typically it appears after large doses or chronic use, although in rare cases some people may become psychotic after relatively small doses. Other chemicals or drugs which similarly increase dopamine function (such as cocaine and L-DOPA) can produce similar psychotic states. Because of this, the term stimulant psychosis is sometimes preferred.
Amphetamine psychosis can include delusions, hallucinations and thought disorder. This is thought to be largely due to the increase in dopamine and perhaps serotonin activity in the mesolimbic pathway of the brain caused by amphetamine-like drugs, although other factors such as chronic sleep deprivation may also play a part. The link between amphetamine and psychosis is one of the major sources of evidence for the dopamine hypothesis of psychosis.
The link between amphetamine and psychosis was first made by Young and Scoville in 19381 and was originally considered to be a rare condition. As amphetamine use increased after World War II, largely due to the widespread use of amphetamine compounds in nasal decongestant and dieting preparations, it became clear that chronic amphetamine use often led to psychotic symptoms.
Hallucinations are frequently reported in chronic amphetamine users, with over 80% of users reporting the presence of hallucinatory experiences2, typically as visual or auditory experiences. Delusions, paranoia, fears about persecution, hyperactivity and panic are also reported as the most common features3
Concurrent to having delusions and hallucinations, chronic amphetamine users may also display stereotyped, repetitive and seemingly purposeless movements, known as 'motor stereotypies' or more commonly as 'knick knacking', 'tweaking' or being 'hung-up'. These may include examining, sorting, disassembling, and cleaning.  The article on punding gives a more complete description of this behavior. This behavior may be similar to the symptoms of  OCD.
One particular manifestation of psychosis associated with amphetamine use is delusional parasitosis or Ekbom's syndrome, where a person falsely believes themselves to be infested with parasites. However, related behaviour may occur in non-psychotic conditions, where users will realise they are not infested by parasites but will pick at their skin anyway. This more closely resembles obsessive-compulsive disorder.

# Amphetamine psychosis in popular culture
There is a chapter in Hunter S. Thompson's Fear and Loathing in Las Vegas entitled 'Aaawww, Mama, Can This Really Be the End?... Down and Out in Vegas, with Amphetamine Psychosis Again?', a reference to Bob Dylan's Stuck Inside of Mobile with the Memphis Blues Again.
In the film Requiem for a Dream, Sara Goldfarb, one of the four main characters clearly suffers from amphetamine psychosis after having been prescribed amphetamines as a weight loss drug, specifically, hallucinations of her refrigerator trying to devour her.
The meth song is a drug awareness public service announcement that has become part of popular culture.
The film A Scanner Darkly (as well as the novel of the same name) contains a scene where the character Charles Freck suffers from formication.
The anti-drug advertising of the Montana Meth Project often focuses on the dangers of amphetamine psychosis.