From Signal to System: The Next Challenges for Psychedelic Therapies

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The regulatory environment for psychedelic drug development changed significantly throughout 2026, most notably in July when the  US Food and Drug Administration (FDA) finalized its guidance for clinical investigations of psychedelic drugs.¹ At the same time, the Department of Health and Human Services and the Department of Veterans Affairs announced a broader collaboration around research, clinical protocols, workforce preparation, real-world evidence, and the potential future deployment of approved rapid-acting psychiatric treatments.² The Health Resources and Services Administration (HRSA) also asked how these therapies might eventually be delivered in ambulatory clinics, rural settings, and medically underserved communities.³

All of this represents clear progress across many impactful levels, but it is also where the easy part ends.

In my previous blog, I wrote that accelerated review does not lower the evidentiary bar. A priority voucher, rolling submission, or compressed review timeline may allow a promising program to move faster, but speed does not simplify the science. It pulls difficult questions forward and gives sponsors less room to answer them later.

A shorter runway still requires the same aircraft to take off safely.

The FDA’s final guidance gives the field a clearer map. But as drug developers know, the map is not the terrain. The real terrain includes patients who do not fit neatly into protocol criteria, clinical sites with varying levels of experience, subjective effects that resist simple safety coding, federal and state scheduling requirements, and a healthcare system that is not yet configured to deliver these therapies at scale.

The discussion is also moving beyond post-traumatic stress disorder (PTSD).

Veterans and PTSD have appropriately brought urgency and visibility to psychedelic development. But the field is now moving well beyond a single diagnosis or molecule. Pharmaceutical companies are currently exploring psilocybin for treatment-resistant depression and major depressive disorder (MDD), alongside lysergide-based programs for generalized anxiety disorder (GAD) and MDD.

These diagnoses may be separated in clinical protocols, but patients rarely present that way. A person may present with longstanding generalized anxiety, then develop a major depressive episode after years of poor sleep, impaired function, and social withdrawal. Another may meet criteria for both PTSD and MDD, with trauma-related symptoms, hopelessness, suicidality, and chronic anxiety all reinforcing one another. Large epidemiologic studies have consistently shown substantial comorbidity among depressive, anxiety, and trauma-related disorders, with many patients meeting criteria for more than one condition.

That overlap complicates development. Which condition is primary? Which endpoint best captures benefit? Is improvement in depression driven by reduced anxiety, better sleep, fewer trauma symptoms, or a broader change in function? And if one diagnosis improves while another persists, how should the treatment effect be interpreted?

MDD, Treatment Resistant Depression (TRD), GAD, and PTSD may overlap clinically, but they are not interchangeable development populations. The patient who has failed multiple antidepressants is different from the patient with broader MDD who may still respond to established treatment, just as chronic generalized anxiety differs from trauma-linked fear and hyperarousal. That overlap also reinforces why the molecule cannot be viewed as the entire treatment. A patient whose depression improves may still carry severe worry, avoidance, trauma responses, or interpersonal and functional consequences that require diagnosis-specific psychotherapy. Current treatment guidelines include psychological interventions across these conditions, including CBT and combined medication-plus-psychotherapy approaches for depression, CBT-based interventions for GAD, and evidence-based psychotherapies as a central component of PTSD care.^{4, 5, 6} 

For psychedelic development, the question is therefore not simply whether the drug reduces the primary scale score. It is whether the overall treatment model recognizes the patient sitting in the room. The molecules, dosing models, endpoints, psychotherapy or psychological-support requirements, durability expectations, and eventual place in care may differ considerably. A psychedelic session may open a door, but many patients will still need skilled therapeutic work to understand what surfaced, address the coexisting disorder, rebuild function, and reduce the likelihood that old patterns simply return.

The field is therefore moving beyond whether psychedelic therapies can produce a signal. It is asking whether they can produce reliable, durable benefit in patients whose illnesses do not respect the clean boundaries of a clinical trial protocol.

The next phase of psychedelic development will require us to move from signal to system. Sponsors must demonstrate not only whether a treatment produces an acute effect, but for whom, for how long, under what clinical conditions, and with what plan when the disease returns.

Among other things, depression has taught us repeatedly that the disease often does return.

Depression is Not One Patient Population

MDD is frequently discussed as though it is one condition with a predictable sequence of treatment. Start with one antidepressant. Try another. Add psychotherapy or augmentation. Move to a more intensive treatment if the first approaches fail. Eventually, the patient may be classified as treatment resistant.

Clinical reality rarely follows that stepwise framework. One patient may be experiencing a first severe depressive episode. Another may have lived with recurrent depression for twenty years. One may have stopped two antidepressants because of adverse effects. Another may have received multiple adequate courses, augmentation, psychotherapy, and still remain profoundly ill. A third may carry depression alongside anxiety, trauma, chronic pain, substance use, sleep disturbance, or suicidality.

We can no longer use one diagnostic label for patients who arrived at the same destination by very different roads.

This becomes especially important in TRD because resistance itself is not one biological state. A treatment failure may reflect an inadequate dose, insufficient duration, poor adherence, intolerability, an incomplete diagnosis, or true pharmacologic nonresponse.

Those histories are not interchangeable.

One company is exploring psilocybin for a treatment-resistant population already defined by inadequate response to prior treatment. Another is pursuing a broader MDD population, where many patients may be earlier in the treatment pathway and may still respond to established therapies.

For the former, the central question is whether a limited number of administrations can produce meaningful and durable benefit in patients who have already shown that conventional treatment has not been enough.

For the latter, the question is broader. Where should psilocybin sit in an MDD treatment pathway that already includes relatively inexpensive oral medications, psychotherapy, transcranial magnetic stimulation, esketamine, and ECT?

A broader indication creates a larger potential population, but also a more demanding comparison. The therapy is not entering an empty field but a crowded kitchen. Some existing treatments are imperfect and require daily use or repeated clinic visits. Others have serious adverse effects or lose effectiveness over time. But they are familiar to physicians, integrated into payer policies, and supported by decades of clinical experience.

A psychedelic therapy must therefore offer more than novelty or speed. It must demonstrate where it belongs and why the added complexity is justified.

The distinction between MDD and TRD is not semantic. It determines who should receive the therapy, when they should receive it, what the comparator should be, how much uncertainty is acceptable, and how regulators and payers will interpret the eventual evidence.

Standard Depression Treatments Work, but Often Only While We Keep Treating

The durability question is not unique to psychedelics. It is the problem that has followed depression treatment for decades. Antidepressants can work and so can psychotherapy along with esketamine, transcranial magnetic simulation (TMS), and electroconvulsive therapy (ECT) for patients with severe or treatment-resistant illness.

But producing an initial response and keeping a patient well are two different scientific problems.

The standard antidepressant model is built around continued exposure. A patient usually takes medication every day through the acute phase and, if improvement occurs, continues treatment for months or longer to reduce the risk of relapse.

In simple terms, the treatment may still be working because the treatment is still being given. That is not a criticism. Many chronic conditions require ongoing therapy. We do not expect an antihypertensive tablet taken in January to control blood pressure in July after it has been discontinued.

Depression, however, creates an additional expectation. Patients are not seeking only suppression of symptoms. They are hoping to regain emotional range, concentration, relationships, productivity, sleep, confidence, and the ability to live without watching constantly for the next episode.

The STAR*D experience demonstrated both the value and the limitation of sequential antidepressant treatment: patients could achieve remission after trying additional strategies, but the likelihood of remission declined and relapse became more common as more treatment steps were required.⁹

A good reminder that each unsuccessful treatment narrows the path.

We can think of it as trying several keys in the same lock. The first opens the door for some patients. A second or third may work for others. But patients who remain unwell after repeated attempts are not simply a larger version of the original population; they are clinically more difficult to treat.

The same acute-versus-maintenance divide appears with faster and more intensive treatments. Esketamine can produce relatively rapid improvement, but the approved treatment model does not assume that a few administrations permanently alter the course of depression. Treatment begins frequently and generally transitions to ongoing weekly or every-other-week maintenance depending on response.

Continuation pharmacotherapy after successful ECT has also shown the importance of active relapse prevention. In one randomized controlled trial, relapse was frequent after ECT, particularly without active continuation treatment, and combined nortriptyline plus lithium was more effective than placebo or nortriptyline alone in reducing relapse.¹⁰ A later multisite study comparing continuation ECT with continuation pharmacotherapy found both strategies useful, although relapse remained substantial in each group.¹¹

Psychotherapy can provide more durable skills and coping strategies for some patients, but access, adherence, provider quality, and the severity of the underlying illness all influence outcome. TMS may produce sustained benefit in some patients but repeat or maintenance courses are also part of clinical practice.

In other words, depression treatment already lives with a familiar bargain: we can often create short-term improvement, but maintaining it may require continued medication, repeated procedures, ongoing therapy, or some combination of all three.

Psychedelic therapies enter this field with a very different proposition. The promise is not simply that symptoms may improve quickly. It is that one or a limited number of administrations may produce benefit extending well beyond the direct pharmacologic exposure.

This possibility  is certainly compelling but also raises the evidentiary bar.

If a conventional antidepressant loses effect after discontinuation, the response may be to restart it, adjust the dose, change treatment, or add another therapy. If a psychedelic is administered once or twice and symptoms later return, the field must determine whether this represents expected disease recurrence, loss of treatment effect, inadequate initial response, or the need for a planned maintenance strategy.

The relevant comparison is therefore not psilocybin versus placebo at one early point.

It is psilocybin versus the complete depression-treatment pathway.

How long does improvement last after the drug is no longer pharmacologically active? How many patients remain in remission without continuous medication? How many require rescue therapy? How many need another administration? Does re-treatment reproduce the original benefit? Does the interval between treatments remain stable, or does it become shorter over time?

And perhaps most importantly, does the patient merely score better on a depression scale, or does the person actually return to work, reconnect with family, sleep normally, and resume ordinary life?

A short-term signal is clearly needed but durability determines whether the treatment has changed the course of the illness.

From Durability to Delivery

That is where the next set of development questions begins. If the first challenge is proving that a psychedelic therapy can produce meaningful benefit, the next is proving that the evidence can be trusted, the treatment can be delivered consistently, and patient safety can be assessed before, during, and after administration. In the next blog in this series, we will look more closely at functional unblinding in psychedelic trials, why structure around psychedelic administration is important, and how sponsors should think about safety assessments in a treatment model where the experience itself is part of the clinical challenge.

References

1. U.S. Food and Drug Administration. Psychedelic Drugs: Considerations for Clinical Investigations; Guidance for Industry; Availability. Federal Register. 2026;91 FR 43101. Published July 14, 2026.
2. U.S. Department of Health and Human Services. HHS & VA Announce Bold, Comprehensive Partnership to Advance Rapid-Acting Mental Health Treatments for Veterans. Published July 13, 2026.
3. Health Resources and Services Administration. Request for Information: Training and Care Delivery Models for Safe Administration of Potential FDA-Approved Psychedelic Therapies in Ambulatory Clinical Settings. Federal Register. 2026;91 FR 43103. Published July 14, 2026.
4. Kessler RC, Chiu WT, Demler O, Walters EE. Prevalence, severity, and comorbidity of 12-month DSM-IV disorders in the National Comorbidity Survey Replication. Arch Gen Psychiatry. 2005;62(6):617-627.
5. Kessler RC, Sonnega A, Bromet E, Hughes M, Nelson CB. Posttraumatic stress disorder in the National Comorbidity Survey. Arch Gen Psychiatry. 1995;52(12):1048-1060.
6. National Institute for Health and Care Excellence. Depression in adults: treatment and management. NICE Guideline NG222. Published June 29, 2022; reviewed January 30, 2026.
7. National Institute for Health and Care Excellence. Generalised anxiety disorder and panic disorder in adults: management. Clinical Guideline CG113. Updated June 15, 2020.
8. Department of Veterans Affairs and Department of Defense. VA/DoD Clinical Practice Guideline for Management of Posttraumatic Stress Disorder and Acute Stress Disorder. 2023.
9. Rush AJ, Trivedi MH, Wisniewski SR, et al. Acute and longer-term outcomes in depressed outpatients requiring one or several treatment steps: a STAR*D report. Am J Psychiatry. 2006;163(11):1905-1917.
10. Sackeim HA, Haskett RF, Mulsant BH, et al. Continuation pharmacotherapy in the prevention of relapse following electroconvulsive therapy: a randomized controlled trial. JAMA. 2001;285(10):1299-1307.
11. Kellner CH, Knapp RG, Petrides G, et al. Continuation electroconvulsive therapy versus pharmacotherapy for relapse prevention in major depression: a multisite study from the Consortium for Research in Electroconvulsive Therapy. Arch Gen Psychiatry. 2006;63(12):1337-1344.