A wide range of drugs can cause psychosis, from street stimulants like methamphetamine and cocaine to everyday prescriptions like corticosteroids and Parkinson’s medications. The key symptoms are hallucinations, delusions, or both, and they can appear during active drug use, during intoxication, or during withdrawal from certain substances. Some drug-induced psychotic episodes resolve within days. Others persist for months or, in roughly 28% of cases, eventually lead to a diagnosis of a longer-term psychotic disorder like schizophrenia.
Methamphetamine and Cocaine
Stimulants are among the most common triggers of drug-induced psychosis. At least 60% of people dependent on methamphetamine or cocaine experience psychotic symptoms of some type. The mechanism is a flood of dopamine and the signaling chemical glutamate in the brain’s cortex, which overwhelms the brain’s ability to regulate its own signals. The result is often paranoia, auditory hallucinations, and delusions that can closely resemble schizophrenia.
Methamphetamine psychosis was originally thought to clear within a week of stopping the drug, but follow-up studies paint a different picture. While the majority of symptoms resolve within a month, about 30% of people with meth-induced psychosis still have symptoms at six months. Between 10% and 28% report symptoms persisting beyond six months. If psychosis continues after six months of abstinence, clinicians may consider a schizophrenia diagnosis instead.
Cannabis and High-Potency THC
Cannabis-related psychosis has become a growing concern as THC concentrations have risen. The risk scales dramatically with both potency and frequency of use. In one study comparing people experiencing a first psychotic episode with healthy controls, daily users of high-potency cannabis (the type with 12 to 18% THC and virtually no protective cannabidiol) were about 12 times more likely to be in the psychosis group. Even less-than-daily use of high-potency strains carried roughly a sixfold increase in risk.
Lower-potency cannabis resin, which typically contains 2 to 4% THC along with a similar proportion of cannabidiol, carries a much smaller risk. The difference matters because cannabidiol appears to partially counteract the psychosis-promoting effects of THC. Many modern cannabis products are bred for maximum THC with minimal cannabidiol, shifting the risk profile considerably compared to what was available decades ago.
Cannabis-induced psychosis also has one of the highest rates of conversion to a longer-term psychotic disorder. In a large study tracking outcomes over six years, the overall conversion rate from any substance-induced psychosis to schizophrenia spectrum disorder was 27.6%. Cannabis-induced psychosis and psychosis triggered by multiple substances carried the highest conversion risk, particularly among younger men.
PCP, Ketamine, and Dissociative Drugs
Dissociative anesthetics like PCP (phencyclidine) and ketamine produce psychotic symptoms through a different brain pathway than stimulants. These drugs block a specific type of receptor involved in signaling between brain cells. The cells most sensitive to this blockage are the inhibitory neurons that normally keep brain activity in check. When those neurons are suppressed, the result is a cascade of unregulated glutamate and dopamine release in the prefrontal cortex, the brain region responsible for reasoning, planning, and distinguishing reality from imagination.
What makes PCP and ketamine particularly relevant to psychosis research is that they produce not just hallucinations and paranoia but also the “negative” symptoms seen in schizophrenia: social withdrawal, flattened emotions, and disorganized thinking. Stimulant drugs tend to mimic only the paranoia and hallucinations. This broader symptom profile is why dissociative drugs have been central to scientific models of how schizophrenia works at the brain level.
Alcohol and Sedative Withdrawal
Alcohol and benzodiazepines don’t typically cause psychosis while you’re taking them. The danger comes when a person who has been using them heavily suddenly stops. Chronic alcohol use reshapes the brain’s balance between calming signals and excitatory signals. The brain compensates for the constant sedation by ramping up its excitatory activity. When alcohol is removed, that excitatory system is suddenly unopposed, producing a state of dangerous overstimulation.
Alcohol hallucinosis, featuring primarily auditory hallucinations and paranoia, can appear within 48 hours of the last drink and usually resolves within 72 hours. The more severe form, alcohol withdrawal delirium (formerly called delirium tremens), typically appears 3 to 8 days after cessation. It involves hallucinations, disorientation, fever, rapid heart rate, and agitation, and it is a medical emergency. Benzodiazepine withdrawal can follow a similar pattern, though the timeline may be longer due to the slower clearance of certain benzodiazepines from the body.
Corticosteroids
Steroids prescribed for inflammation, autoimmune conditions, and organ transplant rejection are a well-documented cause of psychosis, and the risk climbs sharply with dosage. At doses below 40 mg per day of prednisone (or its equivalent), the rate of acute psychosis is around 1.3%. Above 80 mg per day, that rate jumps to 18.4%. In one study of lupus patients treated with steroids, 32% of the treatment group developed severe psychosis compared to just 3.8% of those not receiving steroids.
Steroid-induced psychosis can include grandiose delusions, paranoia, and hallucinations. It often catches people off guard because they associate steroids with physical side effects like weight gain or bone thinning, not psychiatric ones. Symptoms generally improve once the dose is reduced, but managing the underlying condition that required steroids in the first place makes tapering a careful balancing act.
Parkinson’s Medications
Drugs that boost dopamine activity in the brain are the foundation of Parkinson’s disease treatment, but they come with a significant psychiatric tradeoff. In a study of 198 Parkinson’s patients on long-term levodopa therapy, 22.2% developed psychotic complications. These ranged from simple visual hallucinations (often with the person aware the hallucinations weren’t real) to more complex symptoms including persistent delusions and chronic confusion.
Patients who were older when their Parkinson’s disease began faced higher risk. Those with more complex psychotic symptoms, like delusions, tended to have started the disease younger but used the medication for a longer stretch before symptoms appeared. They were also more likely to experience involuntary movements, another sign of dopamine overstimulation in the brain.
Anti-Malarial Drugs
Mefloquine, an anti-malarial drug, carries warnings for neuropsychiatric side effects including psychosis. The UK’s medicines regulator has strengthened its warnings, noting that psychiatric symptoms like nightmares, acute anxiety, and confusion should be treated as potential warning signs of a more serious event. Because mefloquine has a long half-life, adverse reactions can persist for several months after the last dose. People with any history of psychiatric conditions, including depression or anxiety disorders, should not use mefloquine for malaria prevention.
How Long Drug-Induced Psychosis Lasts
For most people, the psychosis resolves relatively quickly once the triggering drug is out of their system. In a follow-up study of 189 patients treated for psychosis linked to illicit drug use, 60% recovered within one month of stopping. Another 30% took one to six months. The remaining 10% had symptoms lasting beyond six months, and nearly half of that group eventually received a schizophrenia diagnosis.
Several factors predicted a slower or incomplete recovery: a family history of mental illness, starting drug use at an earlier age (when the brain is still developing and more vulnerable to damage), and a longer total history of drug use before the psychotic episode. Repeated emergency admissions for substance-induced psychosis also increased the likelihood of eventually being diagnosed with schizophrenia spectrum disorder or bipolar disorder.
The conversion rate from substance-induced psychosis to bipolar disorder was much lower, at 4.5% over six years, and was more common in women than men. For schizophrenia spectrum disorders, the 27.6% six-year conversion rate underscores that while most drug-induced psychosis is temporary, it sometimes marks the beginning of a longer psychiatric condition, particularly in people who were already biologically vulnerable.