The Bloom #173 Free Edition long-term follow-up

The psychedelic research landscape continues to evolve at a remarkable pace. Last month, I tracked 193 new studies and added the 11 most significant ones to our database. In this monthly recap, I've synthesized what we've learned from these latest findings.

Two standout studies examine the long-term outcomes from both clinical trials and observational research. The durability of psychedelic effects represents a critical area of investigation—one that features prominently in our upcoming report on psychedelics and reimbursement frameworks across Europe.

A brief preview: this comprehensive report (to be published later this month) spans approximately 200 pages, though you'll be able to navigate directly to sections most relevant to your interests. My co-author Martin Gisby will debut these findings at Breaking Convention, consistently one of the most fun psychedelic conferences in the field. I hope to connect with many of you there.

Now, let's explore this month's research highlights.

Floris - Founder of Blossom

ps Join me at Breaking Convention 2025 at the University of Exeter this April 17-19. Use code BLOSSOM10 for 10% off your ticket.

Latest Psychedelic Research

1 Acute Effects and Pharmacokinetics of LSD after Paroxetine or Placebo Pre-Administration in a Randomized, Double-Blind, Cross-Over Phase I Trial​

This randomized, double-blind, cross-over study (n=23) investigates LSD (100μg) effects after daily paroxetine (SSRI) or placebo administration in healthy participants. It finds paroxetine reduced negative LSD effects ("bad drug effect," "anxiety," "nausea") while maintaining pleasant effects, and caused higher LSD concentrations (1.4-1.5x) due to CYP2D6 inhibition, suggesting no LSD dose adjustment is needed when combined with CYP2D6-inhibiting SSRIs.

2 Results From a Long-Term Observational Follow-Up Study of a Single Dose of Psilocybin for a Treatment-Resistant Episode of Major Depressive Disorder​

This one-year observational follow-up study (n=66) examined the long-term outcomes of psilocybin (25 mg, 10 mg, 1 mg; COMP360) in treatment-resistant depression (TRD). Median time to depressive relapse was longest in the 25 mg group (92 days) compared to 10 mg (83 days) and 1 mg (62 days), with most participants relapsing by week 12. A post hoc analysis of those entering the follow-up study (n=58) found a more pronounced difference, with the 25 mg group maintaining benefits for 189 days. Adverse events were minimal, with one case of mild suicidal ideation in the 1 mg group.

3 Acute psilocybin and ketanserin effects on cerebral blood flow: 5-HT2AR neuromodulation in healthy humans​

This single-blind, cross-over study (n=28) using MRI in healthy participants found that psilocybin (18.2mg/70kg) significantly decreased cerebral blood flow (CBF) and internal carotid artery (ICA) diameter. In contrast, ketanserin (20mg) had no significant effect. This finding suggests an asymmetric 5-HT2AR modulatory effect on CBF and provides the first in vivo human evidence of psilocybin-induced ICA constriction.

More Research

• ​Single-Dose Psilocybin Therapy for Alcohol Use Disorder: Pharmacokinetics, Feasibility, Safety, and Efficacy in an Open-Label Study​
• ​A review of psychedelics trials completed in depression, informed by European regulatory perspectives​
• ​Psilocybin alters visual contextual computations​

New on Blossom

1 Psychedelic Research Recap February 2025​

In February, three studies advanced our understanding of psychedelic treatments. An open-label trial found that a single dose of psilocybin (25mg) helped people with severe alcohol use disorder, reducing heavy drinking days by 37.5% and decreasing daily alcohol consumption over 12 weeks, with only mild side effects reported.

Another study revealed that people taking SSRI antidepressants may not need to discontinue their medication before psychedelic therapy. The research showed that paroxetine reduced negative LSD effects like anxiety while preserving beneficial aspects of the experience, despite increasing LSD blood levels by 40-50%.

Looking at mechanisms, researchers used MRI to discover that psilocybin decreases cerebral blood flow and internal carotid artery diameter, while a serotonin 2A receptor blocker had no comparable effect, suggesting an asymmetric relationship that may help explain psychedelics' therapeutic effects.

2 Psychedelic Research Links 2025​

A comprehensive overview of all psychedelic research that has come out this year. We cover the research per month and provide a one-sentence summary for each new publication. After the full summary is added, a link to Blossom's review is added to the papers included in our database.

3 Schizophrenia (Topic Page)

Schizophrenia affects approximately 24 million people worldwide, representing about 0.3% of the global population. Current standard treatments primarily involve antipsychotic medications combined with psychosocial support, though roughly 30% of patients show limited response to existing medications.

Recent research into psychedelic compounds for schizophrenia treatment has entered early clinical trials, with most studies in Phase I/II stages. Due to concerns about psychosis risk, researchers have focused on non-hallucinogenic compounds like ketamine and selective serotonin receptor antagonists. Biotech companies are actively developing novel psychedelic analogues designed to improve patient outcomes while minimising side effects, and continued interdisciplinary research using advanced neuroimaging techniques is expected to drive future breakthroughs in personalised treatments.
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Spotlight

1 Breaking Convention (Conference)

Breaking Convention returns to the University of Exeter from 17-19 April 2025, bringing together scientists, researchers, artists and curious minds interested in psychedelics. This three-day conference offers talks by leading researchers, panel discussions, workshops and artistic performances that explore different perspectives on the psychedelic experience.

What makes this gathering particularly valuable is the diverse mix of attendees from different disciplines - you might find yourself in conversation with a neuroscientist, therapist and someone who approaches psychedelics from a spiritual perspective, all in the same day.

Whether you're interested in the therapeutic potential of psychedelics, their cultural significance or simply have a personal curiosity, this is a welcoming space to learn and connect. Remember to use code BLOSSOM10 for 10% off your ticket.

ps The afterparty last time was amazing, and I hear it's going to be an even bigger celebration this time around!

Molenvaart 76, Anna Paulowna, NH 1761AL
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