Long-term adverse experiences following psychedelic use can persist for weeks, months, or even years, and are relatively unexplored in psychedelic research. Our convergent mixed-method study gained quantitative and qualitative data from 608 participants who reported extended difficulties following psychedelic experiences. Data was gathered on the context of use, the nature and duration of the challenges they experienced (including a written description of these), plus a range of possible risk factors and perceived causes. The most common forms of extended difficulty were feelings of anxiety and fear, existential struggle, social disconnection, depersonalization and derealization. For approximately one-third of the participants, problems persisted for over a year, and for a sixth, they endured for more than three years. It was found that a shorter duration of difficulties was predicted by knowledge of dose, drug type and lower levels of difficulty reported during the psychoactive experience, while a narrower range of difficulties was predicted by taking the drug in a guided setting. Implications for psychedelic harm reduction are discussed.

Rationale: Previous research demonstrating that lysergic acid diethylamide (LSD) produces alterations in time perception has implications for its impact on conscious states and a range of psychological functions that necessitate precise interval timing. However, interpretation of this research is hindered by methodological limitations and an inability to dissociate direct neurochemical effects on interval timing from indirect effects attributable to altered states of consciousness.Methods: We conducted a randomised, double-blind, placebo-controlled study contrasting oral administration of placebo with three microdoses of LSD (5, 10, and 20 μg) in older adults. Subjective drug effects were regularly recorded and interval timing was assessed using a temporal reproduction task spanning subsecond and suprasecond intervals.Results: LSD conditions were not associated with any robust changes in self-report indices of perception, mentation, or concentration. LSD reliably produced over-reproduction of temporal intervals of 2000 ms and longer with these effects most pronounced in the 10 μg dose condition. Hierarchical regression analyses indicated that LSD-mediated over-reproduction was independent of marginal differences in self-reported drug effects across conditions.Conclusions: These results suggest that microdose LSD produces temporal dilation of suprasecond intervals in the absence of subjective alterations of consciousness.

Despite the general consensus that synaesthesia emerges at an early developmental stage and is only rarely acquired during adulthood, the transient induction of synaesthesia with chemical agents has been frequently reported in research on different psychoactive substances. Nevertheless, these effects remain poorly understood and have not been systematically incorporated. Here we review the known published studies in which chemical agents were observed to elicit synaesthesia. Across studies there is consistent evidence that serotonin agonists elicit transient experiences of synaesthesia. Despite convergent results across studies, studies investigating the induction of synaesthesia with chemical agents have numerous methodological limitations and little experimental research has been conducted. Cumulatively, these studies implicate the serotonergic system in synaesthesia and have implications for the neurochemical mechanisms underlying this phenomenon but methodological limitations in this research area preclude making firm conclusions regarding whether chemical agents can induce genuine synaesthesia.

Psychedelic induced mystical experiences have been largely assumed to drive the therapeutic effects of these substances, which may in part be mediated by changes in metaphysical beliefs. However, there is growing evidence that psychedelic experiences can also trigger long lasting distress. Studies of persisting difficulties suggest a high prevalence of ontological challenges (related to the way people understand reality and existence). We conducted semi-structured interviews with 26 people who reported experiencing existential distress following psychedelic experiences. We explored the phenomenology of participants’ difficulties and the ways they navigated them, including what they found helpful and unhelpful in their process. Thematic analysis revealed that participants experienced persistent existential struggle, marked by confusion about their existence and purpose and preoccupation with meaning-making. Along with cognitive difficulties stemming from the ungrounding of their prior frameworks for understanding, participants’ ontologically challenging experiences also had significant emotional, social, bodily and other functional impact. Participants managed to alleviate their distress primarily through ‘grounding’: practices of embodiment and the social and cognitive normalisation of their experience. Our findings suggest that psychedelic experiences act as pivotal mental states that can facilitate transformative learning processes, challenging and expanding the ways individuals make meaning. This research contributes to the growing field of psychedelic integration by exploring the complex pathways through which people reestablish coherence and grow following ontologically challenging psychedelic experiences.

Background and Aims: Little is known about individual differences in Hallucinogen Persisting Perceptual Disorder (HPPD). This study investigated visual processing style and personality across two HPPD types (HPPD I and HPPD II) and a Non-HPPD group. Methods: An online survey was delivered to participants sourced from online HPPD and psychedelic user groups and forums (N = 117). Using one-way ANOVA, respondents were compared across four measures of individual difference. Using logistic regression, a range of visual symptoms and experiences were investigated as potential predictors of group categorisation. Results: The HPPD I group had higher absorption and visual apophenia scores than the other groups and was predicted by higher drug use. The HPPD II group showed significantly higher trait anxiety than both other groups. Across the HPPD groups, HPPD II categorisation was also predicted by increased negative precipitating experiences, lack of prior knowledge and pre-existing anxiety diagnoses. Conclusions: Anxiety, negative precipitating experiences and lack of prior knowledge are associated with negative experiences of persistent visual symptoms following hallucinogen use, whilst higher absorption and visual apophenia are associated with positive or neutral experiences. Together these findings indicate that differences in personality may play a role in determining an individual's experience of HPPD, highlighting the role of individual difference research in expanding knowledge around HPPD.