I would classify HPPD as widely harmless. If you poll non-users you'll find that many people have HPPD like effects and can't recall ever not having them. Seeing a slight trail behind a bright fast moving object is inconsequential in life.
Brains are quite nonlinear. I wonder how many people already had visual artifacts and assorted weirdness, but never paid attention to them because the brain just paves over it, until an experience highlights those artifacts, and now they can't not notice them.
Many people with psychedelic-induced HPPD report them being a difficulty, though. Take this case study:
>These symptoms persisted for the last 13 years, with little change in intensity and frequency. All efforts at treatment, psychopharmacological as well as psychotherapeutic, failed to alleviate the symptoms. Often the patient was unable to focus properly with her eyes and tired rapidly while performing intense visual tasks – these deficiencies being detrimental to her studies and professional work as an architect. As a consequence, the patient became depressed with latent suicidal impulses. She also found it increasingly difficult to distinguish between ‘normal’ and ‘ abnormal’ perceptions.
This papering over of side effects that people insist on is why so many are so hesitant to legalize these drugs. It's doing no favor to the cause when so many refuse to acknowledge the danger that's inherit in some kinds of psychoactive drugs.
There are a couple of things to keep in mind here:
1. The link between psychedelic use and persisting minor visual disturbances is reasonably well established.
2. The link between psychedelic use and serious, problematic visual disturbances or psychiatric issues is not well established at all, and modern evidence calls into question[1].
Even if we do take at face value the attributions of problematic HPPD to psychedelics (which we really shouldn't), the prevalence of this phenomenon is extremely low. So low that there isn't much in the way of empirical data to estimate its prevalence - just case reports. And case reports are a notoriously unreliable way to reason about etiology.
>2. The link between psychedelic use and serious, problematic visual disturbances or psychiatric issues is not well established at all, and modern evidence calls into question[1].
You are misinterpreting this. This is saying there's no link between psychedelic use and increased cases of psychosis. That isn't the same as debilitating HPPD, or any depression/anxiety caused as a result. In fact in that same article he highlights this;
>But he has concerns about Krebs and Johansen’s overall conclusions, he says, because individual cases of adverse effects use can and do occur.
>For example, people may develop hallucinogen persisting perception disorder (HPPD), a ‘trip’ that never seems to end, involving incessant distortions in the visual field, shimmering lights and coloured dots. “I’ve seen a number of people with these symptoms following a psychedelic experience, and it can be a very serious condition,” says Grob.
