How to read a paper on the short-term impairing effects of cannabis: A selective and critical review of the literature

Author Michael A White, Nicholas R Burns Published August 15, 2022 Abstract The prosecution of cannabis-presence driving offences (in the absence of any behavioural evidence of impairment) is ultimately based on the assumption that there is a tight causal relationship between positive toxicology for cannabis and impairment. The main purpose of this review is to  …

Legal psilocybin prescriptions in Canada

What is the Special Access Programme? On January 5th 2022, Health Canada amended the Food and Drug Regulations and the Narcotic Control Regulations to allow previously excluded ‘psychedelic’ drugs such as Psilocybin to be included on the ‘Special Access Programme’ (SAP). The SAP allows healthcare practitioners to request limited access to drugs that are not  …

Comparative harms assessments for cannabis, alcohol, and tobacco: Risk for psychosis, cognitive impairment, and traffic accident

Author Petter Grahl Johnstad Published July 25, 2022 Abstract Researchers have associated cannabis use with risk for psychosis, cognitive impairment, and traffic accident. However, this review shows that the association between moderate cannabis use and psychosis is no stronger, and often considerably weaker, than the corresponding association for moderate tobacco use. The same holds for  …

State naloxone co-prescribing laws show mixed effects on overdose mortality rates

Author MaryKate Duska, Jared M. Rhoads, Elizabeth C. Saunders, Tracy Onega Published July 25, 2022 Objective To examine the relative changes in opioid overdose mortality rates between states that have and have not adopted naloxone co-prescribing laws. Methods We performed a synthetic control analysis. National Vital Statistics data for the years 2012–2018 were analysed, and  …

Eating ourselves to death: How food is a drug and what food abuse costs

Author Matthew Robinson Published July 18, 2022 Abstract The objective of this paper is to examine definitions of the terms “drug,” “drug use, “drug abuse,” and “addiction” to determine if the most commonly consumed foods in America are similar or consistent with drug use, abuse, and addiction. The methodology consists of reviewing published studies in  …

The Misuse of Drugs Regulations 2001: A case study in poor legislative drafting

Author Cathal T Gallagher Published July 11, 2022 Abstract The Misuse of Drugs Regulations 2001 (MDRs) create exemptions to the offences of possession, production, supply, and administration of controlled drugs (CDs), which are necessary to allow healthcare professionals to treat patients without rendering themselves liable to prosecution for various offences under the Misuse of Drugs  …

Cannabinoids and the endocannabinoid system in fibromyalgia: a review of preclinical and clinical research

Authors Stephanie Bourke, Anne Schlag, Saoirse Elizabeth O’Sullivan, David Nutt, David Finn Published May 21, 2022 Fibromyalgia affects millions of people worldwide and has a significant impact on quality of life. Fibromyalgia symptoms include persistent widespread pain, fatigue, stiffness, sleep disturbances and cognitive dysfunction. Endogenous cannabinoids (endocannabinoids), the body’s own marijuana-like transmitters, are involved in  …

Characteristics of People Seeking Prescribed Cannabinoids for the Treatment of Chronic Pain: Evidence From Project Twenty 21

Authors Anne Katrin Schlag, Michael Lynskey, Alan Fayaz, Alkyoni Athanasiou-Fragkouli, Brigitta Brandner, Barbara Haja, Elizabeth Iveson and David J. Nutt Published June 14, 2022 Medical Cannabis for Chronic Pain Chronic pain is a pervasive, and potentially disabling condition. In the UK it is estimated to affect between one third and one half of the adult  …

The Post COVID cathinone hydra

Written by Professor Fiona Measham and Dr Michael Pascoe A study published in the journal of Drug Science Policy and Law describes tumultuous changes to the UK MDMA drug market following Brexit and COVID-19 lockdowns. In this first academic publication from The Loop’s ‘back of house’ testing service, nearly half of substances sold as MDMA were  …

A critical review of drug testing policy in the Philippines

Authors Carissa Paz Dioquino, Carissa Paz Dioquino Published May 16, 2022 Abstract The drug policy in the Philippines is written as the Comprehensive Dangerous Drugs Act of 2002 or Republic Act 9165. Unlike drug policies in other countries, the law includes policies on drug testing. Aside from mandatory drug testing for specific situations, the law  …

Farmability and pharmability: Transforming the drug market to a health-and human rights-centred approach from self-cultivation to safe supply of controlled substances

Authors Fabian Pitter Steinmetz, Maja Kohek Published May 3, 2022 Background The supply chains addressing the global demand for major recreational drugs are hardly addressed due to international contracts, particularly the UN Single Convention on Narcotic Drugs. Currently applied regulatory changes have several disadvantages ranging from political tensions to the neglect of ecological aspects. The  …

UK Drugs Inquiry: Drug Science Response

In 2019, Drug Science submitted evidence to the Drugs Policy Inquiry by the Health and Social Care Committee. In 2020, we prepared a detailed report in response to the Dame Carol Black Drugs Review. In 2021, we reacted to the government’s 10-year Drug Strategy. Our 2022 response to the UK government’s call for evidence of  …

Secondary School Educational Resources

For far too long school students have been denied access to the truth about drugs, which has undermined their trust in health information in general and put them at greater risk of harm. This new initiative sets out to rectify this failure by presenting teaching materials that are evidence-based, balanced and proportionate. In this way,  …

Can psilocybin be safely administered under medical supervision? A systematic review of adverse event reporting in clinical trials

Authors Jeremy Roscoe, Olivia Lozy Published March 16, 2022 Psilocybin is a naturally occurring psychoactive chemical produced by various species of mushroom, mainly in the psilocybe genus. Human consumption of psilocybin, primarily for its psychoactive properties, dates back thousands of years (Tylš et al., 2013). It was first isolated in 1958 by Albert Hoffmann, who was later  …

Why doctors have a moral imperative to prescribe and support medical cannabis—an essay by David Nutt

Authors David J Nutt Published January 26, 2022 “Medical cannabis has been legal to prescribe since 2018—yet just a handful of prescriptions have been made in three years. The reasons: stigma, fear, and an entrenched resistance in the medical profession that is harming patients” Prof David Nutt – Founder of Drug Science The field of  …

Drug Policy Explained: Legalisation, Decriminalisation, and Prohibition

By Leah Williams What is Drug Policy In law, a policy outlines the rules and guidelines for an act or behaviour. Drug policy explains the different sanctions, criminal or civil, that an individual will face if they break the rules or fail to follow the guidelines around recreational drugs. The government put these sanctions in place in  …

Global Drug Survey 2022 is Live!

The available data for drug-related trends in the UK, and around the world, is extremely lacking. Crime surveys and national statistics have a narrow scope due to the limited data which they collect. Enter the Global Drug Survey (GDS), which collects data directly from people who have experience with drugs and which has become an  …

Professional Perspectives on Treatment for Substance Use Disorders with Mental Health Problems

Authors Ben Houghton, Alexis Bailey, Christos Kouimtsidis, Theodora Duka, Caitlin Notley Published November 25, 2021 Background Opioid-related deaths are at record levels in the UK and contribute to over half of all drug-related deaths. The prevalence of psychiatric disorders within people who uses substances is known to be considerably higher than the general population, yet  …

Medical Cannabis for Epilepsy - Research Summary and Recommendations

Two Years of Research Drug Science research, conducted over the past two years and in close collaboration with the affected families, clearly shows the immense benefits of medical cannabis treatment for these patients. In contrast to the current BPNA guidance stating that prescribing medical cannabis is probably not in the best interests of children, our  …

chemical structure of phencyclidine (PCP) molecule

PCP stands for phencyclidine or phenylcyclohexyl piperidine, and is a dissociative anaesthetic (similar to ketamine) causing a wide range of effects including hallucinations, feelings of euphoria, and of being disconnected from one’s environment. Street names include angel dust, hog, and peace pills.

PCP was discovered in 1926 and was marketed as a general anaesthetic from the 1950s. It was limited to veterinary use in 1967 due to side effects in humans such as dysphoria, hallucinations and poor muscle relaxation. Veterinary use was also suspended in 1978 after the discovery of ketamine

Illegal production of PCP began in the 1960s and it emerged as a recreational drug. Recreational use became more widespread throughout the 1970s but has become less common since.

PCP can be found as an oil, liquid, powder, pill or crystal. It is most commonly smoked, often mixed with cannabis or tobacco, but can also be insufflated (snorted), taken orally (as a pill or powder), or injected.

When smoked with cannabis or tobacco, the usual dosage is 1-10mg of PCP, while tablets usually contain between 1-6mg. When taken orally or inhaled, 10mg of PCP can produce sedation, whereas when injected only 0.25mg is needed.

Taking PCP by injection is strongly advised against. This is because very low doses are required to cause effects meaning there is a higher risk of overdose.

As production is unregulated, it is difficult to know the exact dose being taken. There is also a poor relationship between PCP intoxication and the blood serum concentration of PCP in patients, meaning we have a limited understanding of safe doses of PCP. It is thought that doses greater than 10mg usually result in mild coma and doses of 25mg or more can result in deep coma, convulsions and even death.

PCP action is not entirely understood but is thought that it mainly acts as an N-methyl-D-aspartate (NMDA) receptor antagonist, meaning the drug blocks the action of glutamate at NMDA receptors. PCP also stimulates an enzyme called tyrosine hydroxylase resulting in an increase in dopamine, norepinephrine and serotonin production. Dopamine and serotonin production is associated with many other hallucinogenic drugs and could be responsible for the hallucinations and euphoria caused by PCP. At high PCP doses, strong NMDA antagonism results in complete analgesia and anaesthesia.

The effects, onset time and duration are dependent on the dose taken and the route of administration.


Onset time:

Effects are usually felt anywhere between 15-60 minutes after oral consumption, but are felt just 2-5 minutes after inhalation.



The effects of PCP usually last between 6 and 24 hours but could be up to 48 hours.



The effects of PCP are numerous and highly variable but are often summarised using the mnemonic RED DANES: rage, erythema (red skin), dilated pupils, delusions, amnesia, nystagmus (uncontrolled lateral eye movements), excitation and skin dryness. Effects may vary depending on dosage.


Low doses (2-5mg, orally ingested):

  • Euphoria
  • Hallucinations
  • Dissociation – feeling of detachment from your body/surroundings
  • Sadness, anxiety, paranoia, confusion – often felt in waves
  • Numbness – as the analgesic effects begin
  • Unpredictable behaviour
  • Aggressive or violent behaviour
  • Reduced pain sensation


Moderate to high doses (5-25mg, orally ingested):

  • Confusion
  • Further reduced pain sensation
  • Stupor
  • Mild coma – often occurs at doses greater than 10mg


Very high doses (>25mg, orally ingested)

  • Convulsions – uncontrolled shaking
  • Deep coma with no response to pain
  • Death – can be caused by complications as a result of inhibited pain response (e.g. burns or drowning in a bath), violent behaviour, hyperthermia, hypothermia (e.g. falling asleep outdoors in cold weather), and breathing problems


Comedown: Some users may feel a comedown as the drug wears off. This may last for around 24 hours and feels similar to a hangover. Symptoms can include nausea, headaches and trouble sleeping.



Chronic users can develop a higher tolerance to PCP with frequent use, meaning that they need increasingly higher doses to experience the same effects.

Since the use of PCP as a medical anaesthetic for humans was replaced with Ketamine in 1965, and then later for animals, there have been no reported medicinal uses of PCP.

Some of the effects of PCP can have dangerous consequences, resulting in long-lasting mental effects, physical injury or even death. Although these usually only occur at high doses, it is important to know the risks.


Risks include:

  • Analgesia (loss of pain sensation)
    • This can lead users to hurt themselves, either intentionally or without knowing, and may mean that they do not seek appropriate help for an injury.
  • Violent/unpredictable behaviour
    • Violent behaviour is often reported in people intoxicated with PCP, and is one of the leading causes of death.
  • Cardiovascular effects
    • PCP can cause hypertension (high blood pressure) and tachycardia (fast heart rate). These are usually mild but can be severe in rare cases, and cardiac arrest has been reported following PCP intoxication.
  • Kidney damage
    • Rhabdomyolysis is seen in roughly 2.5% of people admitted to hospital with PCP intoxication. This is when myoglobin is released from the muscles into the blood stream causing damage to the kidneys, or even kidney failure.
    • The exact causes are unknown but could occur as a result of intense muscle contractions caused by PCP or due to PCP acting directly at the muscles.
    • Rhabdomyolysis can be identified by dark, reddish urine and sore or weak muscles and requires immediate medical attention.
  • Overdose
    • As previously mentioned, we have a poor understanding of safe PCP limits but it is suspected that doses exceeding 25mg can constitute an overdose.
    • Symptoms of an overdose include: agitation, nystagmus (uncontrolled side-to-side eye movements), prolonged coma, hypersalivation, hypertension, convulsions, opisthotonos (muscle spasms causing arching of the back and neck), respiratory depression and catatonia (awake but unresponsive).
    • Immediate medical attention is required if a PCP overdose is suspected.

Long term mental effects of PCP use include:

  • Chronic use can lead to acute anxiety, depression and psychosis.
  • Toxic Psychosis
    • Some PCP users experience psychosis after the effects of PCP have worn off. This can involve hallucinations, paranoid delusions and delusions of influence or religious grandiosity.
    • These symptoms often disappear after a few days but can last from weeks to months, requiring treatment. A psychotic state lasting for more than 2 months may indicate that a pre-existing psychosis has been exacerbated.
    • Schizophrenic-like syndromes have been reported in PCP users after chronic low-dose use as well as after single use.
  • Users have also experienced symptoms of frontal lobe syndrome such as speech impediments and memory loss long after taking PCP, as well as ‘flashbacks’, which is when users experience the feeling of being on PCP long after the drug has worn off.
  • PCP can cause changes in NMDA binding in the hippocampus that remain after PCP use. This may be responsible for altered speech and memory, and psychosis.

As PCP has a sedative effect, it should never be mixed with other depressants, such as alcohol, benzodiazepines or opioids, as this can increase risk of coma. Mixing with depressants can also lower your heart rate and breathing to dangerously low levels.

PCP can be addictive. Chronic users may find it difficult to give up and can develop a higher tolerance to PCP with frequent use meaning that they need increasingly higher doses to experience the same effects.

Addicts may also experience withdrawal symptoms when they stop taking the drug. Short-term withdrawal symptoms include high body temperature, seizures, agitation, muscle twitching and hallucinations. These effects can appear a while after the PCP wears off as the drug can remain in the body for around eight days. Long-term withdrawal symptoms may include depression, memory loss, cognitive dysfunction, impaired speech and weight loss.

We know little about whether any health conditions could make PCP more dangerous. However, there are a few pre-existing conditions that are suspected to increase the risk of some of the more dangerous effects of PCP.

It is suspected that a pre-existing psychotic disorder may increase the likelihood of toxic psychosis following PCP intoxication. It is also possible that other mental health conditions such as anxiety or depression could be exacerbated by PCP use. It has also been suggested that being prone to aggression could make PCP users more likely to exhibit violent behaviour while on PCP. Youth previous psychiatric problems may also be risk factors.

Little is known about whether pre-existing conditions of the cardiovascular system (e.g. high blood pressure, arrhythmias) can make PCP more dangerous. However as PCP is a cardiac irritant, users with conditions that put them at increased risk of cardiovascular problems should be cautious of using the drug.

PCP is classified as a Class A drug under the UK Misuse of Drugs Act and as Schedule II under the United States Controlled Substance Act. This means it is illegal to possess, supply or produce PCP in the UK and USA.

Low doses

PCP gets more dangerous with higher doses. Doses of less than 5mg are considered low and tend not to produce most of the more dangerous symptoms.


Sober sitter

The dissociation, hallucinations and delusions caused by PCP can be confusing. Taking PCP with a sober sitter present, rather than alone, can help users to maintain their grip on reality and manage dangerous or unpredictable behaviour.



PCP can cause unpredictable and potentially violent behaviour, and the loss of pain sensation can cause users to injure themselves. Staying in a safe and familiar environment, away from things that might cause injury can reduce the chance of harm.


Don’t combine with sedatives or depressants

As PCP can have sedative effects, combining with other sedative or depressants (e.g. alcohol, benzodiazepines, opioids) can increase risk of coma and cause depressed breathing and heart rate.


Know the signs of overdose

Symptoms of an overdose include: agitation, nystagmus (uncontrolled side-to-side eye movements), prolonged coma, hypersalivation, hypertension, convulsions, opisthotonos (muscle spasms causing arching of the back and neck), respiratory depression and catatonia (awake but unresponsive). If you recognise any of these in yourself or someone else, seek medical attention.


Stay hydrated

PCP can cause increased body temperature. Dehydration can be avoided by drinking water.


Don’t inject PCP

When taken by injection, very low PCP doses are required to cause effects meaning there is a much higher risk of overdose.


Don’t use often

Some of the more dangerous or long-lasting side effects of PCP become more common with frequent use.

PCP makes people violent

Violent behaviour is often associated with PCP use however the actual prevalence of PCP-induced violence is debated.

Many who disagree with the idea that PCP makes people violent point out that the majority of research into PCP and violence works with PCP users who have been incarcerated or hospitalized and could only represent the more extreme examples of PCP abuse. Additionally, when PCP users in the general population are studied, many authors agree that violence in PCP users is much less common than is portrayed in the media.

Some people also suggest that only certain risk factors cause PCP users to become violent while intoxicated. McCardle and Fishbein found that PCP users who exhibit violent behaviour tend to be younger, have more psychiatric hospitalizations and are generally more aggressive whether intoxicated or not.

There is limited research that investigates the connection between PCP use and violence, and studies often have methodological weaknesses and produce contradictory findings. Therefore we cannot determine the extent to which PCP induces or exacerbates violent behaviour and it is worth considering that this is still a possibility when taking the drug.

Support our work and help ensure that evidence-based research can influence policy and public opinion, not political or commercial agenda.

Drug Science is an independent, science-led drugs charity. We rely on donations to continue to promote evidence-based information about drugs without political or commercial interference.

We are grateful … But we need more. We can’t do it alone. Becoming a donor will help ensure we can continue our work. Join our Community and access opportunities to become more deeply engaged in our work.

Project Twenty21 - September Update

Get Project Twenty21 Updates via Email Last month saw Drug Science’s festival debut as we took up a stand alongside our medical cannabis friends from PLEA, Medcan Support and MedcannID at the incredible Product Earth Expo. We gave away hundreds of stickers, badges and posters to help spread the word about medical cannabis and Project Twenty21.  …

Students “End the Stigma” around medical cannabis this Freshers Week and improve access for young patients

Order Printed Materials Print at Home Materials As UK students look forward to an ‘in person’ Freshers Week this September, the research and policy charity Drug Science has enlisted the help of student ambassadors to help spread the word about the potential benefits of medical cannabis, and tell the honest and factual truth about drugs  …

Managing kratom dependency with Buprenorphine during covid-19: A case report

Authors: Rosalind Gittins & Samantha Cole Published: July 19, 2021 This paper describes a case report where buprenorphine was successfully used for the management of kratom (Mitragyna speciosa) dependency during the Covid-19 pandemic in a specialist community substance misuse treatment service. The individual had a notable iatrogenic dependency on oral over the counter and prescribed  …