Study Finds Up To 9% Of Psilocybin, LSD Experiences Lead To Flashbacks

Those who have consumed psilocybin or LSD may be familiar with the experience: the day after your trip, it’s back to reality, but there are still glimmers of your previous day’s trip, a fleeting visual cue that adapts to the more intense hallucinogenics based on effects you have just experienced .

These spontaneously recurring drug-like effects after hallucinogenic exposure are called flashback phenomena; Symptoms may include blurred vision, mood swings, and derealization/depersonalization. Individuals with persistent recurrent flashbacks that cause significant distress or impairment may have hallucinogen-persistent perception disorder (HPPD), which is considered extremely rare.

New research published in the journal Psychopharmacology further examines psychedelic flashbacks, with results from six placebo-controlled studies showing the phenomena occurred in up to 9.2% of participants after exposure to LSD or psilocybin.

The authors note that although they are believed to be among the “most important side effects of hallucinogenic drugs,” the data and current knowledge on both flashbacks and HPPD are “very limited.” For the study, researchers analyzed data from multiple clinical trials to better describe flashback phenomena and HPPD.

The researchers used data from six double-blind, placebo-controlled studies involving a total of 142 participants aged 25 to 65 years. A total of 90 participants received LSD, 24 psilocybin and 28 both substances. The doses varied by study; Participants received one to five doses of LSD ranging from 0.025 to 0.2 mg and/or between one and two doses of psilocybin ranging from 15 to 30 mg.

Subjects were asked at each study session to report any adverse events since their last contact with the study team, and all events, including flashbacks, were recorded. All studies also included a graduation visit after the last study session, during which all subjects were asked about the occurrence of flashback phenomena throughout the course of the study. Those reporting flashbacks were asked to describe the phenomenon, specifically the quality, quantity, extent of impairment, and time of onset.

Those reporting flashbacks at the end of the study were then followed up via email, specifically to assess the occurrence of continued HPPD flashbacks. Those who reported other flashbacks were again asked to describe them (with the conditions of the visit at the end of the study) along with possible triggers for the flashbacks.

During the final study visit, 13 participants (9.2%) described a flashback experience; seven cases occurred after ingestion of LSD, two after psilocybin, and four after ingestion of both substances. Most flashbacks were visual changes (in 11 of the 13 participants), and three participants experienced other phenomena (such as auditory/cognitive effects or a sense of dissolution). Two participants reported only emotional changes.

The researchers also found that flashbacks were limited to the week after the last drug administration in all but two cases.

Flashbacks lasted from seconds (69.2%) to minutes (23.1%) for most subjects, although one case (7.7%) reported changes lasting hours. The subject indicated that this included increased perception of colors and slowed thinking the day after three study sessions.

In most of these cases (53.8%), the phenomena occurred only once. In two cases (15.4%), symptoms persisted more than five times. One of these subjects reported about 20 visual flashbacks within a short period of about 24 hours after drug administration. The other person experienced approximately 30 visual flashbacks within seven months of drug administration. This was the only patient who clearly reported flashbacks after the end-of-study visit. However, the researchers found that flashbacks lasted only seconds when they were perceived as benign and did not interfere with daily life in either case.

More than 50% of participants reported that the flashbacks occurred while relaxing or just before sleep (meaning 1.4% of all 142 subjects reported distressing flashback experiences). While two participants said the flashbacks were uncomfortable, 10 said they were neutral or positive. The remaining case was not adequately documented. Overall, none of the subjects reported any impairment in their daily life due to these symptoms.

The researchers also noted that none of the participants met criteria for HPPD at any time point, although they noted the rarity of the disorder and the small sample size as factors.

“Drug-like experiences after administration of LSD and psilocybin appear to be a relatively common phenomenon in clinical trials of healthy participants,” the authors concluded, clarifying that these flashbacks were mostly benign and did not interfere with daily life. “Taken together, our data suggest that flashbacks are not a clinically relevant problem in controlled trials of healthy participants.”

Could focusing on flashback symptoms have greater potential in a therapeutic setting? While the study unveils new insights that could help inform further research on the subject, especially as the West continues to embrace psychedelic medicine, there is much more to discover.

The study “Flashback Phenomena After Administration of LSD and Psilocybin in Controlled Trials with Healthy Participants” was authored by Felix Müller, Elias Kraus, Friederike Holze, Anna Becker, Laura Ley, Yasmin Schmid, Patrick Vizeli, Matthias E. Liechti and Stefan Borgwardt .