Hallucinogen Persisting Perception Disorder (HPPD) with Steven Locke, MD, DLFAPA
In this episode of the Psychedelic Medicine Podcast, Steven Locke, MD, DLFAPA joins to discuss the intricacies of Hallucinogen Persisting Perception Disorder (HPPD). Dr. Locke is a former Associate Professor of Psychiatry at Harvard Medical School and past-President of the Society of Biopsychosocial Science and Medicine. Throughout his career, he has focused on mind-body interaction. Since 2019, he has specialized in the evaluation and treatment of persons with persistent perceptual symptoms following use of psychedelic drugs.
In this conversation, Dr. Locke explains HPPD, a relatively rare but potentially debilitating condition in which perceptual disturbances experienced during psychedelic intoxication persist or recur long after the drug has left the body. He describes common symptoms, including visual snow, afterimages, and trails behind moving objects, while discussing what clinicians know - and still don’t know - about the condition’s onset, risk factors, and underlying mechanisms. Drawing on his clinical experience and a survey of more than 1,000 respondents, Dr. Locke explores potential treatment options, including medications and behavioral interventions, and the challenges of finding appropriate care when many clinicians are unfamiliar with HPPD. Throughout, he emphasizes the importance of informed consent, patient education, and further research to better understand the risks associated with psychedelic use and support those experiencing persistent perceptual symptoms.
In this episode, you'll hear:
What HPPD is and how its intermittent and chronic forms differ
What research and clinical experience suggest about the onset of HPPD and potential contributing factors
How HPPD differs from visual snow syndrome and other neurological or perceptual conditions
The psychological impact of HPPD, including anxiety, depression, and fears of having permanently damaged one’s brain
What is known about the long-term course of HPPD and how avoiding further psychedelic use and cannabis may affect symptoms
Quotes:
“There is some thought that there are two different types of HPPD. Type one are intermittent flashbacks, but there are long intervals in between without any visual abnormalities and type two is more chronic with debilitating symptoms and that is the persistent form in which people have what feels to them like permanent changes in their visual system with a variety of symptoms” [8:15 – 8:48]
“A lot of clinicians, even ophthalmologists, don't have a clue what people [with HPPD] are really experiencing. Another phenomenon are after images. Images that persist after some of your visual field sees an object, and then that object moves and goes out of your visual field. But there's a persistence of the image in the visual field. People also report seeing tracers or trails in which as an object moves, a kind of a stroboscopic effect, but it's more smooth, in which there's a trail of an image behind a move, something which moves, the, the trails, seeing trails or traces of objects is among the most frequent of the, of the visual symptoms of people report. And about two thirds of people who have enough symptoms to satisfy the diagnostic criteria for HPPD… will have trails. Following that in frequency would be seeing movement that isn't there. So you're looking at an object and it appears to be moving but you are aware that it couldn't possibly be moving—for example, a building… And another symptom is seeing spots that seem to drift in front of your eye. These are different from floaters… But people will see dots or points or particles that emerge in a dark environment or in an obscure room. People see intensified colors or see overlapping geometric patterns. Sometimes people report seeing unusually sharp color contrasts that seem abnormally intense. People also will report seeing flashes of color that are incompatible with what it is that they're actually looking at. Some people report that they have difficulty reading and sometimes it's because the text on the page seems to move or increase or decrease in size. People also report seeing light where there is no light. There are another half a dozen or so of these symptoms.” [10:48 – 13:34]
“There's a high prevalence in the history of people who develop HPPD of a past history of head trauma. About somewhere between 8 to 10% of people with HPPD, when you take a careful history, it turns out that they have had head trauma, sometimes with loss of consciousness and sometimes without. A small percentage have a history of seizures or epilepsy but not that much greater than what you'd find in the background in the population. Migraine headaches with aura are also reported more often in this population than in the general population, with a prevalence of about between 12 to 15%. And then there's a bunch of other neurological conditions but none at high rates—we don't have enough of a sample to know what the rates are of other neurological conditions.” [15:42 – 16:50]
“Visual snow syndrome is the same visual snow that I described earlier [in patients with HPPD]. It's just that it occurs in people who have no past history of ever using a hallucinogen, a psychedelic, or even cannabis. And so the etiology of that condition is unknown. I think it's on the verge of being classified as a true medical disorder, which would take it from being visual snow syndrome to visual snow disorder.” [17:17 – 17:54]
“Among the people who developed HPPD, about half had used mind altering drugs other than prescription drugs 25 times or more. And another, smaller group of about a third of the population had only tried a psychedelic drug once and even after one exposure developed HPPD. So there's a wide variety in the population that we surveyed… about a third of them said that it developed immediately after the trip—so that the trip ended and the symptoms persisted—and so one of the terms that has sometimes been used to describe HPPD is a trip that never ends… another 20% of people reported that their symptoms began within a week of their having been exposed to a psychedelic drug and an equal number—another 20%—developed between a week and a month. And then those three groups account for about 75% of the population of people. The others are distributed anywhere from four months to—I've had some people that I've seen who developed it 20 years after the last time they used a psychedelic drug… So there's a very small number of people like that. But it's surprising that there can be long intervals of months or years following the elimination of the drug from the body. I mean, the drug is metabolized and broken down and excreted, so it leaves the body. And yet there's some change that has occurred in the mind, in the brain, at the receptors that were where psychedelics interact with the brain. And somehow something has changed, which may not be obvious immediately, but can somehow manifest later in time. We don't have a clue as to what that process is.” [22:15 – 25:13]
“Oftentimes the story that I would hear [from HPPD patients] is [they] went to see an optometrist or ophthalmologist thinking that there was something wrong with their eyes and invariably their eye exam was normal. I actually had one patient who had some eye abnormality but that was really unrelated [to their HPPD]. And then sometimes those patients are then referred to neurologists. And the neurologists oftentimes would do brain imaging studies or EEG studies searching for an epileptiform kind of disorder. Those MRIs, CT scans, and EEGs were invariably normal—well, again, there was one exception: someone who had an unrelated finding in an MRI, which probably had nothing to do with his HPPD. And yet when I see patients, if they haven't had an MRI, I generally will suggest that they discuss with their primary care doctor or the neurologist or psychiatrist who referred them that they should get one, even though the likelihood that it's going to turn up something is very, very low. If it turned up something that was treatable—either a benign tumor or a brain cancer—those treatable conditions need to be addressed. So I think out of thoroughness it's important to rule out the possibility that this is not necessarily related to hallucinogen use.” [32:12 – 33:51]
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