Trip killers: Addressing a critical knowledge gap in psychedelic research

Psychedelic compounds are attracting increasing interest as potential treatments for mental health disorders, while recreational and unsupervised use is also rising. The authors note that although classical psychedelics such as psilocybin and LSD can produce therapeutic experiences, they can also trigger severe adverse states known as “bad trips”, characterised by anxiety, paranoia, perceptual disturbance, and sometimes presentation to emergency services. The paper argues that there is no clear consensus or systematic evaluation of pharmacological options for terminating these experiences, even though such situations are clinically relevant. This review aims to examine the theoretical basis, empirical evidence, pharmacokinetics, and safety profiles of medications that might attenuate or end a psychedelic experience. The authors focus mainly on classic serotonergic psychedelics, especially psilocybin and LSD, but also note relevance to DMT, ayahuasca, and mescaline. They also consider non-pharmacological management and the ethical tension between interrupting a distressing experience and potentially disrupting meaningful psychological processing.

This is a narrative review rather than an empirical study. The authors appear to have synthesised existing literature on candidate “trip killer” medications, including human trials, preclinical studies, case reports, and anecdotal reports from online forums. The extracted text does not clearly specify a formal database search strategy, inclusion criteria, or systematic review methods, so it should not be treated as a systematic evidence synthesis. The review organises the discussion around pharmacological classes and mechanistic plausibility, with particular attention to 5-HT2A receptor antagonism because activation of this receptor is widely accepted as central to the psychedelic state. The authors also discuss non-pharmacological strategies such as psychological containment, environmental calming, and integration, because they argue these should generally be tried before medication unless there is significant risk of harm. Across the pharmacology sections, the authors compare candidate agents on receptor affinity, functional activity, time to peak plasma concentration, half-life, routes of administration, availability, and adverse-effect burden. They evaluate selective 5-HT2A antagonists, antipsychotics, antidepressants, antihistamines, benzodiazepines, niacin, and approaches they consider unhelpful, and then offer provisional recommendations based on the balance of mechanistic plausibility, practicality, and safety.

The review identifies ketanserin as the strongest pharmacological candidate on the basis of both mechanism and direct human evidence. A randomised, double-blind, placebo-controlled crossover trial is described in which ketanserin 40 mg given 1 hour after LSD 100 µg shortened and attenuated acute LSD effects from 8.5 hours to about 3.5 hours without altering LSD pharmacokinetics. The authors also state that ketanserin pretreatment has been shown to prevent the acute effects of LSD, psilocybin, and mescaline, and to reverse LSD effects. They describe ketanserin as dose-dependent in its 5-HT2A blockade and practical in principle, but note its limited availability in some regions and its hypotensive effects. Among other selective 5-HT2A antagonists, pirenperone is presented as a preclinical candidate that completely blocked LSD effects in animal studies, while pimavanserin is described as having high receptor affinity but an unfavourable profile for acute use because of its slow onset, very long half-life, and cost. Ritanserin and piremperone are mentioned as additional candidates, but availability and side effects are limiting factors. Pizotifen is described as potent and widely available, with animal data suggesting attenuation of psychedelic effects, but human evidence is lacking and anticholinergic and antihistaminergic effects are concerns. For antipsychotics, the review states that only agents with substantial 5-HT2A activity are likely to reliably reduce psychedelic effects. Risperidone is highlighted as the most plausible and is described as a first-line option in the authors’ recommendations. Human evidence cited includes a dose-dependent blockade of psilocybin effects, with 1 mg risperidone blocking 98% of effects in pre-treatment. Haloperidol is reported to reduce some subjective effects such as boundlessness, derealisation, and depersonalisation, but not visual hallucinations, and it increased anxiety. Olanzapine, quetiapine, lurasidone, ziprasidone, asenapine, loxapine, aripiprazole, brexpiprazole, paliperidone, clozapine, and chlorpromazine are discussed as possible options with varying receptor profiles, onset times, and side-effect burdens. Quetiapine is described as commonly mentioned in online forums, but the authors suggest its main effect at low doses may be sedation rather than true termination of the psychedelic state. Among antidepressants, trazodone and mirtazapine are portrayed as the more favourable options because of 5-HT2A antagonism, but both are sedating. The text says a single case report and a 24-week pre-treatment study found that trazodone 200 mg daily attenuated the psychological and physiological effects of LSD. Selective serotonin reuptake inhibitors are said to have mixed and uncertain effects, and tricyclic antidepressants are not favoured. Cyproheptadine and promethazine are presented as antihistamines with some 5-HT2A antagonism, but mainly as symptomatic or adjunctive options. Benzodiazepines are described as widely used for acute distress but as not terminating the psychedelic state itself; rather, they provide anxiolysis or sedation. Midazolam, diazepam, lorazepam, and clonazepam are cited as useful depending on setting and route, but the authors caution about addiction, respiratory depression, hypotension, and reduced consciousness. Niacin is described as an unusual candidate: a small controlled study reportedly found that 3 g attenuated LSD effects, and post-LSD administration rapidly reduced effects within 5 minutes, but the mechanism is speculative and the evidence is limited. Alcohol and cannabis are judged more likely to worsen than help a bad trip. Overall, the authors state that the literature is sparse, much of it theoretical, and that the ideal agent would be rapid, selective, easily administered, safe, and short-acting. On that basis, they recommend ketanserin first, risperidone or paliperidone if ketanserin is unavailable, and then cyproheptadine, trazodone, or mirtazapine when neuroleptic sensitivity is a concern.

The authors argue that the management of bad trips should begin with non-pharmacological containment, because difficult psychedelic experiences may still have therapeutic value. They emphasise calm, non-judgemental support, a low-stimulus environment, and later integration. Medication should be reserved for cases in which non-pharmacological approaches are inadequate or unsafe. In their view, the key pharmacological target is the 5-HT2A receptor, because this receptor is central to the psychedelic state. They interpret the evidence as favouring selective 5-HT2A antagonism as the most rational approach to aborting an ongoing psychedelic experience, with ketanserin as the clearest example because it has direct human evidence of shortening LSD effects. They also position risperidone as the most practical antipsychotic option, mainly because it combines receptor activity with availability and multiple formulations. Other agents are discussed as more limited by sedation, long half-life, poor oral practicality, cost, or safety concerns. The authors also note that some antipsychotics, especially haloperidol, may be ineffective or even worsen anxiety during a psychedelic state. The paper repeatedly acknowledges that the evidence base is thin and largely theoretical. Much of the current guidance is inferred from receptor pharmacology, preclinical work, case reports, and anecdotal reports rather than from robust clinical trials. The authors highlight that deliberate induction of bad trips is ethically problematic, which limits research opportunities, although they suggest that future studies could test abortive medication strategies when distress emerges naturally during psychedelic sessions. They also note that poly-substance use and user preferences require further study. In terms of implications, the authors suggest that health systems and clinicians will increasingly need to recognise and manage acute psychedelic distress as use becomes more common. They argue that better evidence is needed for comparative effectiveness, safety, and feasibility across candidate drugs, and that the most effective “trip killer” may require more than simple 5-HT2A antagonism because psychedelic pharmacology is complex.

The authors conclude that increasing unsupervised psychedelic use creates a clear challenge for acute care settings, which are often not designed to support altered states of consciousness. They reiterate that psychological containment and other non-pharmacological measures should be prioritised, but that pharmacological options are needed when safety is at stake. On the basis of the current evidence and theory, they consider ketanserin and certain atypical antipsychotics the most promising choices, with other sedating agents and benzodiazepines serving as secondary or adjunctive options. They end by stressing that healthcare systems will need to adapt as psychedelic use grows, while avoiding premature interruption of potentially meaningful psychological processing.