Hallucinogens: What Are They, Side Effects, Precautions & Abuse

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Medically Reviewed By:
Mark Arredondo, M.D.

Hallucinogenic drugs, also known as psychedelics, have been in the news lately as recent breakthroughs have highlighted their potential health benefits.

Find out what hallucinogens are, how they’re used, and their side effects, precautions and drug interactions. Plus, learn about the signs of hallucinogenic drug abuse.

What are hallucinogens?

The exact definition of hallucinogens is still under debate, according to the National Institute on Drug Abuse (NIDA). Some researchers classify all psychedelic and dissociative drugs as hallucinogens, while others think only some fall under this label.

While the precise definition may still be up in the air, NIDA says hallucinogens include a wide assortment of drugs that alter a person’s thoughts, feelings and awareness of their environment.

Hallucinogens either come from plants or mushrooms, or they’re made in the lab (synthetic). They fall into two categories: classic and dissociative. Some common classic hallucinogens include:

  • LSD
  • Psilocybin
  • Peyote
  • 251-NBOMe
  • DMT

Well-known dissociative hallucinogens include:

What are hallucinogens used for?

“Psychedelics induce the brain to change transiently in ways that appear to allow a reset to take place and permit alterations in previously 'stuck' ways of feeling and thinking about things," Dr. Jerrold Rosenbaum, director of the Center for the Neuroscience of Psychedelics at Massachusetts General Hospital, in Boston, said in an Harvard Health Publishing article. "It's like rebooting your computer."

NIDA says people report using hallucinogens to reduce pain and stress levels, improve feelings of well-being, and to enjoy emotional and spiritual experiences.

Because of hallucinogens' work in changing brain processes, the U.S. Food and Drug Administration (FDA) recently released a statement on clinical trial guidelines for them. It says they show promise for treating:

  • Depression
  • Anxiety
  • Mood disorders
  • Post-traumatic stress disorder (PTSD)
  • Substance abuse disorders

The American Psychological Association (APA) notes psychedelics have shown healing potential for these conditions in several clinical studies.

“Combined with psychotherapy, some psychedelic drugs like MDMA, psilocybin and ayahuasca may improve symptoms of anxiety, depression and post-traumatic stress disorder,” psychologist Cristina Magalhães of Alliant International University in Los Angeles told the APA.

Although study of hallucinogens' effectiveness is ongoing, in 2019 the FDA did approve a psychedelic nasal spray called esketamine for use in treatment-resistant depression therapy.

In addition, the FDA has approved Breakthrough Therapy status for two psychedelics: psilocybin for treatment-resistant depression and major depressive disorder and MDMA for PTSD.

Hallucinogen side effects

According to NIDA, you may experience these side effects when taking hallucinogens:

  • Extreme emotions
  • Floating out-of-body sensations
  • Seeing striking shapes and colors
  • Distorted hearing
  • Reliving memories
  • Shaking
  • Nausea or vomiting
  • Headache
  • Abdominal pain
  • Diarrhea
  • High blood pressure
  • Fast heartbeat

Hallucinogen precautions

NIDA emphasizes that the effects of hallucinogens can be unpredictable and may lead to altered perceptions. This can cause dangerous behavior if you aren’t monitored by medical professionals while taking the drugs.

Unregulated hallucinogens also sometimes contain harmful additives or other drugs.

Some hallucinogens are associated with a rare condition called hallucinogen persisting perception disorder, which is marked by dissociative and psychedelic experiences even when not under the influence of the drug.

Although limited evidence indicates these drugs aren’t addictive, some studies suggest people can build up a tolerance to them over time. Overdose, though uncommon, may occur at high doses or in combination with other substances, especially alcohol.

Research into hallucinogens' use during pregnancy is also limited, although PCP use during pregnancy has been linked to several health conditions in infants.

Hallucinogen interactions

Just as the health effects of hallucinogens are still being studied, so too are their potential drug interactions. Some hallucinogens are thought to work by altering the chemical serotonin. For this reason, NIDA says that they may interact with medications that increase the serotonin levels in your brain.

“There are clinically significant drug interactions between first-line psychiatric medications and psychedelic therapies,” psychiatric pharmacist Dr. Benjamin Malcolm told the website Psychedelic Support. “These interactions could pose major hurdles or increase the risks of psychedelic therapies.”

Before taking hallucinogens, talk to your doctor about these potential drug interactions, Malcolm advises:

  • MAOIs
  • SSRIs
  • Lithium
  • Benzodiazepines
  • Amphetamines
  • CYP2D6 inhibitors
  • 5HT2A receptor blocking antipsychotics
  • Serotonin reuptake-blocking antidepressants
  • Serotonin agonists
  • Alkaline phosphatase inhibitors
  • UGTIA10, IA9 inhibitors

Hallucinogen abuse

Hallucinogen use is increasing among Americans, and in 2019 there were 1.2 million new users, according to the American Addiction Centers. Long-term use can lead to hallucinogen use disorder, which is marked by compulsive or out-of-control patterns of use.

Here are some signs of hallucinogen use disorder:

  • Drug cravings
  • Inability to stop using
  • No longer participating in activities you enjoy
  • Use that gets in the way of home or job responsibilities

The centers note that although hallucinogen use disorder is a risk, it is uncommon.

“More research and discussion are needed to understand the possible benefits of these drugs, and psychologists can help navigate the clinical, ethical and cultural issues related to their use,” Magalhães said.


National Institute of Drug Abuse: Psychedelic and Dissociative Drugs

National Institute of Drug Abuse: Drug Facts: Hallucinogens

Harvard Health: Back to the future: Psychedelic drugs in psychiatry

U.S. Food and Drug Administration: FDA Issues First Draft Guidance on Clinical Trials with Psychedelic Drugs

American Psychological Association: Can Psychedelic Drugs Heal?

U.S. Food and Drug Administration: FDA approves new nasal spray medication for treatment-resistant depression; available only at a certified doctor’s office or clinic

Office of U.S. Congressman Jack Berman: Bergman, Correa Applaud New FDA Guidance to Help Those Suffering from PTSD

Psychedelic Support: Psychedelic Therapy and Psychotropic Medications: Speaker Series with Dr. Ben Malcolm

American Addiction Centers: Hallucinogen Addiction: Types & Effects of Mind-Altering Drugs

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