The symptoms of drug psychosis typically appear suddenly and intensely and include paranoia; hallucinations, possibly violent in nature; and delusions, sometimes about being pursued for drug use. Speech becomes disorganized and incoherent. Those experiencing transient psychosis  may, while experiencing delusions, attempt to act on such delusions and engage in dangerous behavior.
The symptoms can be distressing and terrifying to those who have them— they don’t know what is real and what is not—and may be accompanied by thoughts of suicide. In this altered state of reality perception, people can be withdrawn or agitated, and they may become aggressive, threatening harm to others as well as self. Amphetamines, cocaine, and cannabis are the most common precipitants among drugs of abuse, but prescribed medications such as steroids are also known to precipitate a psychotic episode.
An affected person may speak very rapidly and string together words and sentences that make little outside sense. They may reveal thoughts and perceptions that bear little relation to current reality, strike out at others, or refuse to eat or drink.
While the onset of substance-induced psychosis is typically dramatic, it can also emerge more slowly with subtle shifts in behavior. That does not make them of any less concern. Substance-induced psychosis should be regarded as needing emergency medical intervention.