Psychedelic-assisted therapy has drawn growing attention, somewhere between hope and hype. A public guide from McLean Hospital, a psychiatric hospital in Massachusetts, explains in plain language how it works, which substances are being studied, what results exist and which risks and limits are worth knowing.

What does the guide set out to do?

The guide aims to explain, in accessible language, how psychedelics may treat various mental health conditions, what recent research says, what their legal status is and how the therapy is conducted professionally and safely. It has no named author; the current version lists a physician contributor.

How does it explain the therapy?

It describes psychedelic-assisted therapy as the controlled use of these substances to supplement counselling sessions. In simple terms, it explains that they act on serotonin receptors in the brain, may temporarily disrupt a brain network called the default mode network and may promote neuroplasticity.

It stresses that this is not a one-off dose. The process it describes includes an initial consultation, informed consent, two to three professionally supervised sessions, and integration work and ongoing therapy afterwards.

Which substances does it cover?

The guide covers psilocybin, MDMA, LSD and DMT (including ayahuasca), as well as a dissociative anaesthetic with psychedelic properties that is already used in clinical settings. The mechanisms and status of each are described on our substances under research page, so we do not repeat them here. The evidence and framework for ketamine and esketamine have a page of their own.

What results does it present?

  • Depression. It refers to studies of psilocybin, including one published in 2022 in the Journal of Psychopharmacology with effects lasting up to a year, and a study in JAMA using a single dose combined with psychotherapy.
  • Post-traumatic stress disorder. It describes a 2021 trial with 90 participants in which, at the end, 67% of the MDMA group no longer met diagnostic criteria, compared with 32% of the placebo group.
  • Anxiety and end of life. It states that a single dose of psilocybin can produce lasting reductions in anxiety and mentions existential fear at the end of life, without identifying the studies.
  • Addiction and eating disorders. It refers to preliminary results on alcohol craving and presents the other applications as possibilities, without data.
  • Dissociative anaesthetic. It reports an effect within 24 hours in treatment-resistant depression, but notes that it has generally only been studied for up to six weeks, so long-term effects have not been shown.

Which risks does it point out?

The guide describes difficult acute reactions (panic, intense fear, raised heart rate and blood pressure, nausea) and lists other risks: acute psychological distress, flashbacks, interactions with other medicines, worsening of existing conditions, potential for misuse, which the guide considers unlikely, and a lack of standardised regulation. It also warns about contamination of illegally obtained substances and insists that no one should take them without the support of a trained professional.

It also acknowledges the limits of the research: “However, the therapeutic effects of psychedelics are not yet well understood.” It explains that, even in double-blind studies, participants and investigators can usually tell who received the drug, which may inflate the reported benefits.

What does it conclude?

Its conclusions are optimistic: the guide considers that, although research is at an early stage, psychedelic therapy may become a valuable therapeutic tool and, in time, a recognised and legal treatment option.

How to read this guide

KETAMED commentary. It is a popular-science text without a named author, and some statements appear without references or in simplified form, such as the claim that fewer than 0.1% of participants had adverse effects or the idea that psychedelics increase serotonin levels. Its tone is more optimistic than its title suggests. The 2021 MDMA trial is a randomised, placebo-controlled study, but of modest size; the later US regulatory decision on MDMA, which the guide does not mention, is summarised on our MDMA page.

What it means in Portugal

KETAMED commentary. The legal framework described in the guide is that of the United States only. In Portugal, psilocybin, MDMA, LSD and DMT are controlled substances and are not authorised as medicines; outside authorised clinical trials, they are not available as treatment. On our scientific evidence page we separate what is under research, what has positive results and what is actually approved.