Medically reviewed by Stephanie Hartselle, MD

Hallucinogen persisting perception disorder (HPPD) is the presence of recurring visual disturbances and other symptoms sometime after using a hallucinogen, such as LSD (lysergic acid diethylamide) or PCP (phencyclidine). HPPD can affect mental health and cause ongoing stress and concern.

This article will explain how HPPD happens, describe common symptoms, and provide information on diagnosis, treatment, and ways to cope during an episode.

How Does HPPD Happen?

HPPD can occur after the use of recreational hallucinogenic drugs. Most people experience HPPD symptoms as a flashback (a past incidence that recurs vividly in the mind) or a benign reexperiencing of the initial drug-induced experience.

The mental disorder affects a small percentage of people with a history of psychedelic drug use. The number of people who experience flashbacks shortly following the use of hallucinogens can range from 5% to 50%, but research estimates that between 1% and 3% of people will develop HPPD.

Hallucinogens are drugs that cause a person to perceive things that do not exist or are not present (hallucinations). For example, people may experience physical sensations, sights, sounds, or smells that are not real or present.

Related:What Causes Hallucinations?

Causes

After taking hallucinogenic drugs, some people continue to have postdrug experiences, like flashbacks. While LSD is most commonly associated with HPPD, many other substances can cause it, including cannabis (marijuana), psilocybin (mushrooms), MDMA (Molly or Ecstasy), mescaline, and PCP.

The cause of HPPD is not fully understood. However, research points to various possibilities. Some evidence shows that HPPD is brought on in a similar way as post-traumatic stress disorder (PTSD) symptoms, which develop when a memory is triggered by a similar environmental factor.

Another hypothesis is that HPPD could be caused by deconditioning. This means that once vision and other senses have been altered, they are more likely to occur again without prompting.

Additional research suggests that people with previous traumatic experiences may be more affected by HPPD. This hypothesis says that strong memories could be more easily accessed with psychedelic drug use and mistaken as flashbacks.

Risk Factors

Anxiety is a potential trigger for HPPD. Some people may experience anxiety about having a flashback episode before the symptoms start. Being in a dark environment post-hallucination, using cannabis, and taking certain medications are other factors that can trigger the onset of HPPD.

There is also a correlation between the number of times a hallucinogenic drug is used and the onset of HPPD. Research suggests that using hallucinogens 15 or more times is a risk factor for developing the disorder.

HPPD Symptoms

HPPD causes several symptoms, which can vary from person to person. Usually, people experience symptoms affecting their vision or mood.

The two types of HPPD are:

• Type 1 is characterized as having visual disturbances and an ongoing disruption in perception after having used hallucinogenic drugs.

• Type 2 is defined as having flashbacks of the drug-induced experience.

Vision Symptoms

Common vision symptoms among people with HPPD include:

• Seeing floaters, which are black or gray objects that move with vision

• Seeing trails behind moving objects (palinopsia) or changes in motion perception

• Having pseudohallucinations (sensory experiences vivid enough to be a hallucination but recognized by the person experiencing them as not real)

• Seeing flashes of color or light

• Seeing things as smaller than they are in reality (micropsia)

Other Symptoms

Some people with HPPD may also experience the following:

• Depression symptoms

• Thought disorders, such as schizophrenia or psychosis

• Panic attacks

• Migraines

Diagnosis: Is There an HPPD Test?

If you are experiencing persistent hallucinations following hallucinogenic drug use and believe you may have HPPD, a healthcare provider may assess your symptoms using one of the following tools:

• Vividness of Visual Imagery Questionnaire: A self-reported assessment that asks about vivid memories and visual experiences

• Modified Tellegen Absorption Scale: An assessment that examines your openness to absorbing and self-altering experiences

• Visual Apophenia Luke Irvine Scale: An assessment that uses images of clouds to understand how vividly a person sees different images in them

These assessments alone cannot diagnose HPPD. Talk to a healthcare provider for help interpreting the results of these tests and to determine whether HPPD is the correct diagnosis.

How Do You Treat HPPD Symptoms?

There is little research on the most effective treatment options for HPPD. A healthcare provider may prescribe medication such as benzodiazepines or selective serotonin reuptake inhibitors (SSRIs) to help with symptom management, as these medications have been shown to help some people who experience visual disturbances. Klonopin (clonazepam), in particular, may be effective in treating HPPD.

However, taking certain medications can worsen symptoms in some people. Maintaining close contact with a healthcare provider when determining an effective treatment plan is important.

For most people, HPPD is not reversible. Although many people will see a reduction in symptoms over time, HPDD is still likely to be long-lasting and can persist for many years.

What to Do During an HPPD Episode

During an HPPD episode, it's common to experience stress and anxiety. Finding ways to stay calm can help prevent symptoms from worsening. Here are some things to try:

• Use relaxation techniques, such as deep breathing, yoga, and listening to soothing music.

• Ensure that you are safe, especially if you are experiencing vision disturbances or changes. Avoid driving a car or participating in activities that may compromise your safety.

• Talk to a mental health professional to work through symptoms and process any stress you experience during an HPPD episode.

Summary

HPPD is when a person experiences ongoing visual disturbances, flashbacks, and other persistent symptoms after hallucinogenic drug use. Little research explains what causes HPPD, but certain factors can increase your risk. A healthcare provider can diagnose HPPD based on your symptoms. Treatment methods can vary, and research indicates that benzodiazepines and SSRIs are effective treatment options. HPPD episodes can bring stress and anxiety, so relaxation techniques such as meditation, breathing, and yoga can reduce symptoms or shorten episodes.