For some people, it can happen out of nowhere. The computer screen seems to take on an extra glow; all of a sudden the chair in front of you seems to have shrunk; a subtle web of geometric shapes begins to overtake your field of vision. Flashbacks to former trips are not overly common, but they can be a very real side effect of taking psychedelics. Hallucinogen Persisting Perception Disorder (HPPD) is a rare and unusual outcome of psychedelic exploration.
What is Hallucinogen Persisting Perception Disorder (HPPD)?
Hallucinogen Persisting Perception Disorder (HPPD) is a condition that affects some people who use psychedelic drugs or have used them in the past. People with HPPD have visual flashbacks that mimic the effects of psychoactive drugs—like trailing lights, glowing objects, and floaters. Only, considerable time may have passed since the last use of psychedelics.
These flashbacks occur at random, and they are primarily visual in nature. They can cause some people to feel disoriented or uncomfortable, especially if the flashbacks come at an inconvenient time, such as while driving. Research from the 1980s suggests that between five and 50 percent of people who use hallucinogens have at least one flashback at some point in their lives. However, exactly why some people experience these flashbacks and not others is unknown.
Very little, in fact, is really known about HPPD, although the condition is described in both the primary texts used in psychiatry and general medicine: the Diagnostic and Statistical Manual of Mental Disorder V and the International Classification of Disease. In more recent investigations, scholars recommend dividing HPPD into two distinct types, based on the severity of the symptoms.
HPPD Type 1
HPPD Type 1 is a mild form of hallucinogen persisting perception disorder. Those with this diagnosis tend to have benign visual flashbacks, with little disruption to daily life. Many of the flashbacks patients experience are similar to or the same as what they experienced while on psychedelic drugs. These perception distortions are described as “short-term” and most patients have a positive recovery in time.
HPPD Type 2
HPPD Type 2 is proposed to be more severe, with perception distortions that cause more disruption to daily life. Flashbacks may not always mimic what was experienced during the psychedelic trip. Instead, the brain may hallucinate new visual experiences. In some cases, those with type 2 HPPD have long-enduring flashbacks that require medication to manage—much like a conventional psychosis. Type 2 is also more likely associated with symptoms of depression. This type of HPPD is considered persistent and severe, but exactly how many people develop HPPD Type 2 after psychedelics is unknown.
It’s important to mention, however, that these broad classifications are not widely adopted in the medical space. Instead, medical scientists have put forth these classifications after reviewing and presenting case studies of patients who have HPPD. As it stands right now, only HPPD as a broad disorder is accepted in the standard medical literature.
What Causes HPPD?
HPPD is a relatively mysterious medical condition. It’s unclear exactly what causes HPPD, but it is always linked to the use of psychedelics. Some people develop HPPD after just one trip, while others develop the condition after repeated use of psychedelics. And many different psychedelics can cause these symptoms; evidence suggests that ayahuasca, ibogaine, shrooms, muscimol, peyote, LSD, ketamine, and MDMA may all contribute to some type of HPPD. Cannabis, which is not considered a hallucinogen, is also a potential contributor to HPPD.
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Although some scholars propose that there are two primary subtypes of HPPD, it’s possible that there may be different forms of HPPD depending on which substance triggered the reaction. Indeed, the fact that so many different substances can contribute to HPPD suggests that the mechanisms that underlie the condition are far more complex than what meets the eye. A 2018 paper published in Brain Sciences, for instance, outlines a few leading, but painfully incomplete understandings of the condition.
Currently, the main hypotheses about HPPD focus primarily on LSD. Researchers suggest that HPPD may be caused by alterations in the visual processing center of the brain triggered by an LSD trip. Another hypothesis suggests that LSD may produce such a strong temporary change in the electrical currents in the brain that it alters the functioning of brain cells that regulate neurotransmitters that help filter out unnecessary visual stimuli. Yet another hypothesis suggests that people who are prone to anxiety during psychedelic trips may be more at risk of developing symptoms of HPPD later.
Simply having a “bad trip” certainly does not cause HPPD. But, it’s common for HPPD episodes to have a trigger—a certain event or stimuli that instigates an HPPD episode. In the limited case reports available, cannabis consumption was identified as a potential trigger. Other triggers included stress, dark environments, and stimulated mental states. Of course, potential triggers are unique to every patient.
The limited research on HPPD thus far perhaps does a better job ruling out what doesn’t cause HPPD than what does. For example, researchers know that HPPD is not caused by extensive brain damage from psychedelic substances. Nor is it caused by substances being re-released in the body after being stored in bodily tissues; your first HPPD flashback can occur months after last using a psychedelic.
What is HPPD Like?
HPPD causes visual flashbacks, similar to a visual hallucination. But what may be more accurate to say is that HPPD causes distortions in perception; almost like the brain is interpreting the visual information it’s receiving in an alternate way than usual. An object in motion may appear distorted, for example. Or, you may begin to notice unexpected flashes of color. Although, some people may actually hallucinate things that are not actually there.
Most of the time, people are still aware of their surroundings during these flashbacks, which is actually similar to many different types of visual hallucinations. During an HPPD episode, colors may appear brighter, objects may appear an unusual size, or there may be halos of light around different objects. Visual distortions like trails of light and seeing geometrical patterns are also commonly reported—the same things that happen when you’re tripping.
During these flashbacks, a person may experience periods of uneasiness. But overall, the experiences are limited to visualizations. These visualizations often do not cause impairment, but they can be disruptive and anxiety-provoking. A person may need to sit down, stop driving, or engage in some type of stress-relieving activity while they wait for the episode to pass.
How is HPPD Treated?
For some people, the symptoms of HPPD may be so mild that they choose to forgo treatment and can easily recognize the experience as a psychedelic flashback. But, avoiding a diagnosis can be risky. Visual distortions similar to those caused by HPPD can also have more sinister origins, like a brain lesion or stroke. Many of the visual distortions associated with HPPD are also common in migraine, which is treated with very different medications than HPPD. So, even if symptoms are quite mild, it is important to rule out other potentially serious causes before deciding what actions to take.
Unfortunately, however, those seeking treatment for HPPD should prepare for a journey of trial and error before landing on an effective option; there are no known medical treatments for this condition. But, not all hope is lost—HPPD may be treated with some of the same prescription medications used to treat other hallucinations. Antidepressants, mood stabilizers, antiepileptic, anti-anxiety, and antipsychotic medications are all types of drugs that can be prescribed experimentally for HPPD.
Still, with no known cause, treatment for HPPD patients can be difficult and frustrating. So, many medical providers may recommend lifestyle interventions to reduce the frequency of potential triggers and to help patients cope with episodes when they come up. Talk therapy, behavior therapy, meditation, and treatment for underlying stress, anxiety, and other mental health conditions may go hand-in-hand with treatment for HPPD.
The bottom line? HPPD is still quite mysterious. It’s possible that several different medical phenomena are lumped together under the HPPD umbrella. It’s also possible that some people may be more at risk of developing HPPD than others. Right now, medical professionals know so little about HPPD that there is no standard course of treatment. Researchers have not conducted any clinical trials for effective therapies for HPPD. Instead, most of the treatment information available comes from individual case studies with HPPD patients. Persisting visuals after psychedelics remains an under-explored area of medicine, without a doubt.