Hallucinating Long After the Trip is Over: HPPD – Part 1

An overview of the symptoms of Hallucinogen Persisting Perception Disorder (HPPD), how it differs from flashbacks, and how common it might be.


Psychedelic clinical trials are on the rise and more are on the way as previous studies have generally concluded that psychedelics are safe. Researchers are also aware, however, that they do not come without risks. But are there long-term effects from psychedelics that are harmful in any way?

This is a valid research question but for the general public, it may also echo the 1987 anti-drug commercial showing that your brain can become “fried” just like the egg sizzling away in the pan, irreparably damaged.1

Amanda Feilding, Executive Director of the Beckley Foundation clarifies that “[t]here is no evidence indicating that classical psychedelics can fry anyone’s brain—they are remarkably non-toxic substances, and they have not been associated with any kind of neurotoxicity or organic brain damage.”2

Another legitimate concern is whether you can get stuck in a permanent psychedelic state, forever tripping, or “permatripping”. According to James Fadiman, when Timothy Leary and Richard Alpert actually attempted to sustain a long-term psychedelic state by taking large doses of LSD each day, they were unable to do so.2 This is because consecutive doses of psychedelics such as LSD, psilocybin, or mescaline lead to the development of rapid tolerance, or a decline in response that happens as quickly as a few hours, even if the initial dose is quadrupled.3

Fried brains and “permatripping” may not have any scientific backing, but there are two other risks to psychedelic users: flashbacks and Hallucinogen Persisting Perception Disorder (HPPD).

What is the difference between flashbacks and HPPD?

Flashbacks are brief and benign remembrances of a drug’s effects that occur at some point after the drug has worn off.  During these episodes, people can still function normally and they may experience the flashbacks with pleasure,4 some even referring to them as a “free trip”.5 They can last seconds to minutes and may only occur a handful of times.6

HPPD on the other hand, is a prolonged and distressing visual disorder, lasting from weeks to years after use while impairing daily functioning.7 Unlike flashbacks, HPPD is included in the DSM-V, making it a clinically diagnosable disorder for people who are experiencing severely distressing visual disturbances who may be unable to lead normal day-to-day lives.8

HPPD can be classified as one of two types, where Type 1 consists of milder symptoms that would be more closely associated with flashbacks. Those with this diagnosis have a good prognosis because they can function normally and only experience temporary and sometimes pleasurable memories of their psychedelic experience. Type 2 is more severe, long-lasting, and has a worse prognosis, as the almost constant visual effects become a regular part of a person’s daily life.9

Researchers summarize that these symptoms may be “debilitating, deteriorating, disintegrating, and disturbing,” and “are experienced as overwhelming, terrifying, and horror-filled phenomena.”10 The changes in perception are so striking that it can cause significant impairment and is usually accompanied by distress as well as depersonalization, derealization, and depression or anxiety.8,11

What are the symptoms of HPPD?

HPPD symptoms can vary widely, but some commonly experienced symptoms include12:

  • Visual snow, or grainy field of vision
  • Colors can flash suddenly or be intensified
  • Haloes, auras around people or light sources
  • Trails, an after-image when an object moves
  • Geometric shapes and fractals
  • False perceptions of movement in the peripheral visual fields
  • Seeing things that are larger, smaller, closer, or farther away than they actually are

Research suggests that most (75.9%) HPPD symptoms arise within one week of the initial drug intake while the rest (24.1%) can begin anytime after a month, with the longest interval found by one study to be 20 years.9 Symptoms can be continuous, intermittent, or sudden,5 and can last between weeks and years, or even decades in a few rare cases.13 Auditory and other senses are usually not affected.

Below are two striking accounts of HPPD after ingesting more than one substance at a time.

Gigantic transparent spiders were in my bed; standing in my bedroom. They didn’t move but stayed in the same place. I left the room and went into my bathroom and everything was normal; but going back into my bedroom they were still there.

– Patient describing visual effects one week after taking psilocybin mushrooms, LSD, cannabis and dextromethorphan (DXM) powder.14

Everything around started to pulse and breathe, various patterns appeared and disappeared, my TV began to talk to me again.

– Patient describing effects after smoking cannabis one month after taking hash, psilocybin, and alcohol.15

How common is HPPD?

It is difficult, if not impossible, to say how common the disorder is, though research suggests it is rare. Some researchers have noted that “the data do not permit us to estimate, even crudely, the prevalence of ‘strict’ HPPD.”16 An online survey collected information from 2,455 psychedelic users and found that 4.2% reported drug-free visual experiences significant enough to think about seeking treatment, which is indicative of HPPD.14 Grinspoon and Bakalar estimated that 1/50,000 psychedelic users meet criteria for Type 2 HPPD.17 According to Amanda Fielding, “[HPPD] affects a very tiny proportion of psychedelic users, and less users of this proportion report troubling effects with it.”2 A recent pooled analysis of 142 participants across six studies found that flashbacks were quite common, occurring in up to 9.2% of healthy volunteers, but none met criteria for HPPD.18

It is important to note that HPPD has never been observed in a clinical trial setting. Dr. Matthew Johnson at Johns Hopkins University, explains: “Amazingly, [HPPD has] never been seen in the thousands of participants, either from the older era, from the late 50s to the early 70s, to people in psychedelic studies with LSD, psilocybin, or mescaline. It’s never been seen in the modern era, now with thousands of [clinical trial] participants at a number of centers like ours and throughout the world.”19

Though most psychedelic clinical trials are screening for HPPD, much of the available research is currently only from open label studies, case reports, and surveys. Despite the fact that this disorder seems to only affect recreational users and only rarely, researchers agree that it requires further investigation.

In Part 2 of this article, we’ll look at the causes and risk factors of HPPD and ongoing research  that aims to investigate the mechanism of this disorder.

Headshot of Alexa Julianne

Alexa Julianne works at MAPS to support MDMA-assisted therapy for the treatment of PTSD. As a writer with a background in clinical research, she provides research-based educational articles about psychedelics and their therapeutic potential in the fields of mental health and wellness.


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1 year ago

Very interesting! An honest look at some of the unknowns in this burgeoning field.

1 year ago

… I wouldn’t quote amanda fielding on anything serious, especially hppd.

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