[Related to: Relaxed Beliefs Under Psychedelics And The Anarchic Brain, HPPD And The Specter Of Permanent Side Effects]

I.

Hallucinogen persisting perceptual disorder is a condition where people who take psychedelics continue hallucinating indefinitely. Estimates of prevalence range from about 4% of users (Baggott) to “nobody, the condition does not exist” (Krebs and Johansen). To explore this discrepancy, I asked about it on the 2019 SSC survey. The specific question was:

Hallucinogen Persisting Perceptual Disorder is a condition marked by visual or other perceptual disturbances typical of psychedelic use that continue for weeks and months after coming off the psychedelic, in some cases permanently. Have you ever had this condition?

2,234 readers admitted to having used psychedelics. Of those, 285 (= 12.8%) stated that they had some hallucinations that persisted afterwards. 219 (9.8%) said they’d had them for a while and then they had gone away. 66 (= 3%) stated that they still had the hallucinations (one limit of the study: I don’t know how long it has been since those people took the psychedelics).

But most of these people reported very mild experiences; on a scale from 1-10, the median severity was 2. The most commonly reported changes were more “visual snow” (ie “static” in the visual field), slight haloes around objects, and visual trails. Many people reported that if they stared at a textured area like a carpet long enough, illusory geometric patterns would start to form. Only a few people noticed anything weirder than this. Here are some sample responses:

— It took the form of visual disturbances (patterns, moving patterns, mild hallucinations like seeing a flower growing on a person’s face or seeing the legs of a chair walk). Initially there would be daily incidents. They seemed to be triggered by fatigue or other stress, and I did not like them, which lead to more stress. Exercise helped reduce the stress and make the visual effects go away. The severity and frequency dropped quickly at first and then more slowly over the years, essentially gone after a decade. I have had migraines with ‘fortification figures’ as well; this was different from that. — Perceptual distortions about once a week. Difficulty concentrating for about 6 months. Intense interest in drawing. — Used LSD about twice a month for a period of time when I was 17, and had a very very slight build up of persisting visual distortions. This phase culminated in me taking ~425µg by accident one night, and having a somewhat negative experience, had an ego death sort of thing, experienced strong “time-warping” where my subjective experience of the passing of time slowed down and sped up repeatedly by a large degree. Very strong acid trip. After that night I experienced pretty noticeable breathing on certain textures, like ceiling tiles, and a sort of “bright aura effect” on others, like pebbles. This gradually receded over something like 1-2 years, at which point it was entirely gone. — straight lines often bend! it’s distracting! — If I stare at an object, it’ll appear to slightly sway or move in a circular motion. If I stare at a surface (especially a textured one like a carpet), faint light patterns will develop. I got HPPD the 3rd time I did LSD. I haven’t done anything to treat it, expecting it would go away on its own over time. However, it’s been like 4 years and hasn’t really changed much. I’ve gotten used to it and often forget I have HPPD. I told an optometrist about it one time and he was just like “yeah, happens to some people who do acid.” — Quite concerned. Seen by PCP and opthamologist. Performed a literature review myself and tried clonidine without a large effect. Symptoms have seemed to resolve however. — Persistent discolouration blue-ward or red-ward, depending on *subjective* head orientation, in a pattern of visual field roughly equivalent to the Tetragrammaton. Yes bloody really. Help. — My colour perception was distorted and confusing for some time, perhaps 1-3 years with browns, greens and reds, especially in natural settings (2C* series) I also experienced intense flashbacks consisting of bodily tingling and diffuse feeling of heat for ~10 months after a different psychedelic session. — I see tracers, halos, have increased anxiety, visual snow. Nothing has helped so far. — Very mild but persistent visual distortions. Walls breathing, kaleidoscoping of repeating patterns, etc. Not severe enough to warrant treatment. — Any highly detailed or repetitive surface “breathes” after looking at it for even a few seconds. get glowing patterns when looking at some art, a sort of cycle of different colors being highlighted in sequence. makes eyes open meditation easier; makes “where’s waldo” harder. — Visual snow; when viewing images which contain several different possible interpretations of patterns (eg hex grid on bathroom tile, carpet weaving pattern) my perception of the most salient pattern stutters and vacillates between the top 3-5 possible interpretations. — I hesitated whether to even answer ‘yes’. 15-25 years ago, a period when I occasionally used psychedelics, I would sometimes have mild visual trails or aberrations when I wasn’t on any psychedelics. It never really bothered me. I can still sometimes make stationary patterns swirl or move by staring at them, but I think that’s just normal visual perception, not HPPD. Right?

A Reddit user helpfully illustrated what his (particularly severe) HPPD looked like (note especially the subtle square grid in left picture):

Weird, but not unbearably so. I think this explains the wide variety of prevalence estimates. Many people who take psychedelics will have very minor permanent changes to their vision. Most of them will shrug and get on with their lives. Only the few people whose changes are especially bad, or who get especially neurotic about it, will ever talk to a doctor.

I discussed some of this recently at a colloquium of experienced psychonauts (realistically: a group house full of the kind of programmers who go to Burning Man). Of the ten or so people there, two admitted to HPPD which sounded about as bad as the image above. They’d never really mentioned it before, it hadn’t come up, and they were living normal lives.

I conclude that lots of people you encounter are having mild hallucinations all the time, and it just never comes up.

II.

I want to talk more about Krebs & Johansen, the paper that claims to find HPPD doesn’t exist.

First, it talks about surveys of special populations, like Native Americans using peyote. None of them report HPPD. Plausibly peyote does not cause HPPD (most of the people on my survey blame LSD) or something about the cultural set and setting prevents Native Americans from getting it during ceremonies. I see thedrugclassroom.com suspects this too.

Second, it talks about K&J’s own study, based in the National Survey of Drug Use and Health. Among 130,152 participants, those who have used psychedelics are no more likely to report symptoms than those who have not. But this survey violates one of the cardinal sins of psychiatric questioning – be careful in how you ask questions about psychosis-like symptoms! (see here for more people getting this wrong). K&J base their finding entirely on how people answer the question “Saw vision others could not?” (they don’t give the presumably longer question for which this is an abbreviation). But it is asked after several other questions clearly probing psychotic symptoms, like “felt force taking over your mind?”, “felt force inserting thoughts?”, and “heard voices?” Participants probably assumed (I think correctly; K&J did not write the survey) that the question was asking about more dramatic visions, like visions from God about their destiny or something. The average person whose visual field was 5% more staticky than normal wasn’t going to answer.

Third, it talks about HPPD-like visual hallucinations in people who have never taken psychedelic drugs. It says many people have them. I believe this. At the colloquium I mentioned, someone talked about having some similar staticky symptoms before taking any psychedelics. On my own survey, a few people said things like “I could always make the carpet self-organize into geometric patterns if I tried really hard, but after I took LSD it started happening much more”. I don’t know of any surveys on how prevalent this is, but since nobody has any trouble finding examples, I imagine it’s pretty common. My only argument that this doesn’t disprove HPPD is how many people – including my survey respondents – describe these oddities starting (or getting much worse) right after they use psychedelics. But we have no idea how many totally drug-naive people are just going around with weird visual experiences just because that’s the kind of person they are.

III.

I want to talk about a case study of this last kind of person (as usual, this is a composite with some details changed to protect privacy). Patient of mine for a totally unrelated reason – she had mild depression after a death in the family, wanted to talk it over. Gradually it started coming out that she had an entire spiritual system based on what part of a grid she thought people fell on. It took me a long time to figure out the grid was literal. It was a shape she could see in her vision, all the time, close to a Cartesian plane but with a couple of extra lines and curves on it. It looked similar in spirit to the grid pattern tiled across the sample image above, though not exactly the same.

In terms of her personality – she was very into William Blake, Meister Eckhart, and ecstatic poetry. She dabbled in Wicca and occultism. She had strong opinions on chakras. Her hair was dyed an even brighter shade of purple than the Bay Area median. I was mildly concerned she was going to either join or start a cult, but she never went further than sharing some of her manifestoes about the nature of time-space with her lucky psychiatrist.

This woman had never used psychedelics. But her description of her visual grid matched some HPPD phenomena pretty well.

I still dream of linking individual differences in perception with differences in cognition. So I wonder: psychedelics make you more likely to believe woo, and more likely to have certain classes of visual hallucinations. But some people believe woo without taking psychedelics, and some people have those same visual hallucinations without taking psychedelics. Are they the same people? Do psychedelics move you along a natural axis of variation, maybe from unusually strong priors to unusually relaxed priors? Was my patient the sort of person that the rest of us would become if we took massive doses of LSD every day for years? Did that explain both her perceptual and her cognitive uniqueness?

Start thinking along these lines, and some other become pretty suggestive. How come some New Agey people say they can see auras around people? Are they just lying? Seems like a weird thing to lie about. And a lot of these people don’t sound like they’re lying. Aren’t auras a classic LSD hallucination? I understand they’re not quite as simple as the haloes around lights that HPPD people get; they’re only around people and sometimes the colors seem meaningful. But add something about handwave handwave using a special kind of visual processing for other people handwave synaesthesia, and maybe it’s not totally outside the realm of possibility? Maybe if your priors are so relaxed – ie so far towards the “naturally on LSD all the time” side of the scale – that you believe in auras, then your priors might also be so relaxed that you can see them.

We really don’t know what other people’s perceptions are like. At least, not until I ask a bunch of questions about this on the next SSC survey.