Hallucinogen Persisting Perception Disorder (often shortened to 'HPPD') is a condition in which the subject experiences a lasting alteration of sensory perception, most often emerging after one or more hallucinogenic drug trips.
Symptoms commonly found in cases of HPPD may also arise as a result of certain other conditions, and as such HPPD is partially defined by an inability to determine a diagnosis which better accounts for the symptoms presented.
The typical symptoms are mild hallucinations similar to those experienced while on psychedelics, but occurring in the sober state.
The primary symptoms of HPPD are characterized by the re-occurrence of perceptual disturbances previously experienced while under the influence of a hallucinogen. The effects are often episodic in nature (often described as 'flashbacks'), and can be triggered by thought processes, additional drug use, stress, anxiety or certain environments and sensory stimuli. Although the symptoms most commonly associated with HPPD are visual in nature, they may also present themselves in a variety of forms, and in varying severity.
Symptoms may include:
Although the onset of HPPD (and by definition the nature of its symptoms) are largely associated with use of hallucinogens, it should be noted that the use of hallucinogenic drugs is sufficient but not necessary for clinical diagnosis.
It is relatively normal to experience persisting effects after a psychedelic experience in some cases, but they will usually fade between the period of a few days to a few weeks.
It is important to make the distinction between HPPD and other sets of long-term effects often associated with hallucinogenic drug use, including but not limited to the emergence of mental conditions including thought disorders, changes in personality, or states of psychosis or delirium.
Human eyes are naturally given to certain visual abnormalities, which are commonly attributed to HPPD, but occur for everyone. Many of these effects are somewhat 'parsed out,' and most people don't notice them until asked to pay attention; it is possible the use of hallucinogenic chemicals makes one more prone to noticing these effects.
Eye floaters are naturally occurring effects of the degeneration of the eye, which become more frequent as a person grows older. They are also attributed to several medical conditions, but are not related to HPPD.
Also known as 'blue-sky sprites,' this effect occurs when a person looks at a large blue light (most commonly the sky), and presents as bright dots in the visual field which move rapidly on an unpredictable path before disappearing within a few seconds.
The appearance of this effect is somewhat comparable to 'tracers,' which are a regular visual effect while under the influence of psychedelics.
Visual snow is a persistent visual symptom in which people see static similar to that of an analogue television in parts or the entire visual field. The causes of this effect are unknown, however it is not considered dangerous and its presence alone is not considered to be a symptom of HPPD.
While HPPD is rarely permanent and there is no cure to this day, there are some treatment options available to help manage severe cases. Certain benzodiazepines such as Alprazolam, Clonazepam and Diazepam have been found to help. However, all currently approved treatments work only in allaying the resultant anxiety or stress caused by the resurgent perceptual disturbances, rather than actually stopping the symptoms.
More recently, research into successors has shown some success in actually reducing the symptoms - drugs such as Tolcapone and Levocarb, which are primarily used in the treatment of Parkinson's Disease. These chemicals are not actually approved for use in treating HPPD, however they have been used off-label to do so.
HPPD is a relatively rare condition and in most cases is not permanent, however not a whole lot is understood about the condition. It has been observed that the emergence of HPPD symptoms is more likely to occur with frequent users of hallucinogens than in people who are not using them, or are using them infrequently. To reduce the risk of contracting HPPD, it is strongly advisable to leave ample time between uses of hallucinogenic drugs and to avoid heavy doses.
Unfortunately there is very little reliable data for clinical research into HPPD, since it is a relatively uncommon condition in terms of solid diagnoses. There is some inconsistent data available, mostly comprised of a recreational drug users who are have come forth seeking help - though this is not perfectly useful for study because of the inconsistency of street-drugs.
Certain substances are known (by mostly consistent anecdotal reports) to be particularly prone to having lasting effects, NBOMEs are notable in this regard.