The Possible Gamechanger of COMP360 for Treating Treatment-Resistant Depression
- Anish Marella
- Feb 27
- 5 min read
Updated: Mar 3
Written by Anish Marella
Psychiatric medicine is undergoing a seismic shift as Compass Pathways announces successful results from its second Phase 3 trial evaluating COMP360 for treatment-resistant depression (TRD).
The findings from COMP006 build on earlier results from COMP005, together demonstrating rapid and statistically significant reductions in depressive symptoms in a population where meaningful clinical improvement has historically been difficult to achieve.
Understanding TRD
TRD affects an estimated 4 million adults in the United States alone. It is typically defined as a chronic form of depression in which an individual has tried at least two different antidepressant medications without experiencing significant improvement. Findings from the STAR*D (Sequenced Treatment Alternatives to Relieve Depression) clinical trial found that the chances of achieving remission are essentially halved by the time a patient moves to a third-line antidepressants.
Compared to Major Depressive Disorder (MDD), TRD is far more debilitating. It is associated with significantly longer depressive episodes, a higher likelihood of chronic depression lasting more than 2 years, prolonged time to remission, and higher relapse rates. Importantly, individuals with TRD also face a significantly higher risk of suicide.
Currently, there is only one available drug for TRD in the USA (Spravato). In the UK, the Medicines and Healthcare products Regulatory Agency requires strict supervision for the administration of Spravato as a Schedule 2 controlled substance.
Furthermore, the economic impact of TRD is staggering. The total annual burden of medication-treated MDD in the US has been estimated at $92.7 billion. While TRD patients represent only one-third of all MDD patients treated with drugs, they account for roughly 47% of the total economic burden. Currently the National Institute for Health and Care Excellence (NICE) does not recommend Spravato (esketamine nasal spray) for TRD in England, Wales or Northern Ireland due to cost-effectiveness concerns. This underscores a desperate need for a treatment that works efficiently, reducing the long-term societal and economic burden.
What is COMP360?
COMP360 is a pharmaceutical-grade synthetic version of psilocybin, a naturally occurring psychedelic compound found in over 200 species of fungi.
The drug is not administered as a standalone intervention, but within a unique three-step therapeutic model:
Preparation: Patients meet with a therapist to establish a foundation of trust and set clear expectations for the experience.
Administration: The session occurs in a clinical setting. The patient wears eye shades and listens to a curated playlist while a therapist remains present for the entire duration of the drug’s effects.
Integration: In the days following the dose, the therapist helps the patient process the insights gained during the session and apply them to their daily life.
This structured protocol is necessary because COMP360 is intended to induce an intense, time-limited altered state that may enable psychological change. The therapeutic container is built to manage safety, optimise outcomes, and satisfy regulators.
The Phase 3 Data: COMP005 and COMP006
The results of the two Phase 3 trials (COMP005 and COMP006) together with Phase 2b data represent a robust dataset of over 1,000 participants. Though COMP005 only included USA participants, COMP006 included individuals from Europe and Canada as well as the USA.
In clinical trials for depression, the primary efficacy scale used is the 10-item Montgomery-Åsberg Depression Rating Scale (MADRS), which assesses symptoms like sadness, tension, and appetite. A reduction of 25% in the MADRS score pre/post intervention is considered clinically meaningful.
COMP005 (Single Dose Focus): In this trial, 25% of participants achieved a clinically meaningful reduction in MADRS at Week 6, with that response maintained through 26 weeks after just one or two 25mg doses.
COMP006 (Dose Exploration): This trial confirmed that the 25mg dose remains the "preferred dose," showing a statistically significant difference of -3.8 MADRS against the 1mg control at Week 6.
Importantly, the data suggests that patients can benefit from a re-administration of COMP360. In Part B of the COMP005 trial, over 40% of patients who showed progress but had not yet remitted by Week 6 went into full remission after receiving a second dose.
“The Phase 3 data from Compass Pathways marks a genuinely important moment for the field. A 4-point separation on MADRS may appear modest at face value, but in the context of treatment-resistant depression this sits firmly in line with, if not competitive against existing treatments - of which currently non are uniquely licensed in isolation for TRD. The real signal, however, lies elsewhere. A 40% response rate following just two 25mg doses is unprecedented in TRD populations, particularly given the historical difficulty of shifting outcomes in this group. Crucially, the study did not simply outperform placebo, but also demonstrated meaningful separation from an active 1mg control , an essential methodological bar in psychedelic trials. Perhaps most compelling is the durability of effect, which appears to extend well beyond what we typically observe with ketamine-based approaches or augmenting antidepressants. In short, Compass have met their primary endpoints while beginning to demonstrate something the field has long sought: not just rapid antidepressant effects, but sustained ones. Further data will be key in understanding the full clinical and mechanistic implications and I look forward to seeing those data and the FDA responses which will come this year.”
Safety within both trials
In any trial involving high-risk TRD patients, safety is the primary concern. The safety data from these trials indicate that COMP360 is generally well-tolerated. Common Side Effects included headache, nausea, visual hallucinations, and transient anxiety.
In COMP005, 66% of Treatment-Emergent Adverse Events (TEAEs) occurred on the day of administration, and 88% were resolved within a day. Similar responses occurred in COMP006, with 73% of TEAEs occurring on the day of administration, of which 83% were resolved within a day.
Between both trials, there was a combined 17 Treatment Emergent Serious Adverse Events (TESAEs) from a total of 14 participants. This equates to 5% and 2% of the total participant sample size in COMP005 and COMP006, respectively. The Independent Data Safety Monitoring Board (DSMB) found no evidence of a clinically meaningful imbalance in suicidality between the treatment arms. Serious suicidal ideation was reported in less than 1% of participants, and the only instance of suicidal behaviour occurred in the 1mg control arm, not the high-dose group.
Comparing COMP360 to the current drug on the market
Compared to Spravato, the current leading drug in the USA for TRD treatment, COMP360 seems to offer a significant advantage in terms of treatment burden. A patient on Spravato may need up to 10 treatments to achieve the same effect that COMP360 achieves at Week 6 with just one or two doses. Moreover, while Spravato requires administration every one to two weeks, COMP360 has demonstrated durability lasting at least six months from a single administration cycle.
Conclusion
The FDA has already granted COMP360 "Breakthrough Therapy" designation, a status reserved for drugs that show significant potential over existing options. The company is currently moving through a rolling submission process and expects to complete their full New Drug Application (NDA) by the 4th quarter of this year.
With the Phase 3 program showing that successful results are reproducible, COMP360 is well-positioned to become a leading treatment. The dual clinical benefits of rapid onset and long-term durability demonstrated by COMP360 signal a new, promising blueprint for treating TRD.
