Generalized Anxiety Disorder: A Persistent Burden Despite Standard Treatments

Prevalence and Impact

Generalized anxiety disorder (GAD) ranks among the most prevalent psychiatric conditions. The Mental and Substance Use Disorders Prevalence Study, using clinician-administered interviews from 2020 to 2022, estimated a past-year GAD prevalence of 10.0% among US adults aged 18 to 65, representing approximately 20.2 million people.¹ GAD is chronic and recurrent, and the functional toll is substantial, with impairment across work, social, and physical domains; reductions in quality of life comparable to those seen in major depression; and higher medical costs than in patients without the disorder.² Comorbidity can further magnify the burden, with mood and other anxiety disorders frequently accompanying the diagnosis.³

Comorbidity and Cost Add to the Burden

GAD rarely occurs on its own. In the World Health Organization World Mental Health Surveys, 81.9% of people with GAD met criteria for another lifetime disorder, including a mood disorder in 63.0% and another anxiety disorder in 51.7%.³ GAD also carries higher healthcare costs than anxiety-free populations: pooled controlled cost-of-illness data found direct medical costs were 2.60 times higher (95% CI, 2.01-3.36).⁴

Standard Treatments With Incomplete Results

SSRIs and SNRIs remain the foundation of pharmacologic care, but their efficacy is less than ideal. In a network meta-analysis of double-blind randomized trials, first-line agents such as duloxetine, escitalopram, paroxetine, and venlafaxine roughly doubled the odds of remission compared with placebo, with odds ratios ranging from 1.7 to 2.3.⁵ Despite these odds, only about one-third of patients experience remission during acute first-line treatment, leaving most still symptomatic.⁶ Treatment options have also remained limited, with no pharmacotherapy carrying a new mechanism of action approved for GAD in the United States since 2007.^7,8

Balancing Efficacy and Tolerability

Response is a more attainable target than remission, but it is not guaranteed. An estimated 30% to 60% of patients do not experience any response to first-line treatment,⁶ and among those who do respond, the benefit is modest. A 2025 Cochrane review of 37 randomized trials involving 12,226 adults with GAD found that antidepressants improved response compared with placebo (risk ratio, 1.41; 95% CI, 1.29-1.55), with a number needed to treat of 7.⁹ At the same time, discontinuation because of adverse effects was more than twice as likely as with placebo (risk ratio, 2.18; 95% CI, 1.81-2.61), corresponding to a number needed to harm of 17.⁹ Overall dropout rates were similar between the groups.

Where Standard Care Falls Short

Standard pharmacotherapy helps many patients but leaves many others symptomatic, and the absence of a mechanistically new approval for nearly two decades limits what clinicians can offer those who do not respond adequately. For a condition this common and this persistent, closing that gap remains an unmet need in GAD care.

The Remission Gap in GAD

Serotonin reuptake inhibitors and serotonin-norepinephrine reuptake inhibitors remain the backbone of long-term GAD pharmacotherapy, and they help many patients. Full remission, though, is the exception rather than the rule. In a network meta-analysis of randomized GAD trials, active agents differed from placebo on remission, defined as a HAM-A score of 7 or less, but only by modest odds ratios; across the pooled trials, remission rates on active drugs clustered well below half, leaving a large number of treated patients with residual symptoms.¹ Benefit also tends to accrue over weeks, and patients who do not respond often move through dose increases, switches, and augmentation, each carrying its own tolerability cost.²

Psychedelics as Mechanistic Diversity

What these first-line drugs share is their target. Whether a molecule blocks the serotonin transporter, the norepinephrine transporter, or both, its proximate action stays inside the monoamine system. These drugs are not inert at the level of plasticity: several antidepressants bind the BDNF receptor TrkB and engage neuroplasticity, a mechanism that may help explain both their benefit and their slow onset.³ The newer interest is in agents that engage plasticity more directly and quickly. Preclinical work characterizes classic psychedelics as psychoplastogens, compounds that produce rapid, sustained structural plasticity, including greater dendritic complexity, after a single exposure, an effect that requires activation of 5-HT2A receptors inside the cell rather than only at its surface.⁴

Translating Plasticity to the Clinic

That mechanistic premise has begun to meet clinical data in anxiety. In a phase 2b dose-finding trial, a single 100 microgram dose of DT120 (lysergide) ODT, a 5-HT2A agonist, lowered HAM-A scores by a placebo-adjusted 5.0 points at week 4, the study’s prespecified primary outcome.⁵ The compound is investigational, but it is the first placebo-controlled signal that one administration of a non-monoaminergic agent can shift anxiety symptoms in GAD.⁵

Beyond the Monoamine Paradigm

None of this means the monoamine drugs have failed. They remain first-line, and for many patients they work well. What has changed is that psychiatry now has more than one mechanistic hypothesis to test in anxiety, something it has lacked for a generation. Whether plasticity-based agents produce durable benefit in practice is the question the current trials are investigating.

Comparison of Two Mechanisms for Treating Anxiety

Both drug classes engage neuroplasticity; they differ in route and speed, not in whether plasticity occurs. Sources: Casarotto et al., Cell 2021; Vargas et al., Science 2023; and Robison et al., JAMA 2025.

How GAD Patients Move Through Treatment

A US insurance-claims analysis, presented at APA 2026¹ and recently published,² examined treatment patterns among patients with GAD. In a treatment-patterns sub-cohort of 59,275 patients, switching, discontinuation, and restarting were common. Among patients who discontinued, 42% restarted after a median of 145 days, and 68% of patients who switched therapies had another encounter after 36 days.¹ These patterns point to treatment cycling rather than durable control, in line with the known limits of current first-line options.

The Case for a Different Mechanism

That gap in current first-line therapies provides a rationale for testing agents with a different mechanism. DT120 (lysergide) ODT, an orally disintegrating tablet studied in earlier trials as MM120, is a single dose 5-HT2A agonist, the receptor mechanism that underlies the effects of classic psychedelics. In its phase 2b GAD trial, the 100 microgram dose reduced HAM-A scores by a placebo-adjusted 5.0 points at week 4,³ meeting the prespecified primary endpoint, and advanced into phase 3. DT120 has FDA Breakthrough Therapy Designation for GAD, which is a development status and not an approval.

Early Answers on Safety

Two APA 2026 preclinical posters addressed key safety concerns associated with serotonergic psychedelics. Because DT120 is active at the 5-HT2B receptor, which is associated with valvular heart disease, one study chronically dosed rats and found no lysergide-related changes in heart weight or valve tissue and no evidence of ventricular or valvular remodeling at the doses studied.⁴ A second study assessed abuse and dependence potential. Repeated dosing produced 5-HT2A receptor downregulation consistent with tolerance, and after 25 weeks of weekly dosing the animals showed no evidence of withdrawal or abuse-related behavior.⁵ These animal findings do not establish human safety, but they speak to the two objections most often raised about the class.

What the APA Data Show Together

The APA data frame two halves of the same story. The real-world analysis shows why better GAD treatments are needed, while the preclinical studies begin to test whether a 5-HT2A agonist can be developed without the long-standing cardiac and dependence concerns associated with this class.  The ongoing phase 3 program will determine whether these early findings translate into clinical benefits and an acceptable safety profile.

How the Receptor Switches On

Classic psychedelics, including DT120 (lysergide), act as agonists at the serotonin 2A (5-HT2A) receptor rather than the serotonin transporter blocked by SSRIs and SNRIs. A 2020 structural study captured the active-state 5-HT2A receptor bound to a hallucinogen and coupled to its Gq protein, clarifying how these compounds engage and activate the receptor.¹ The primary target is a receptor, not the serotonin transporter.

A Receptor That Holds On

A crystal structure of LSD bound to the 5-HT2B receptor, together with binding-kinetics experiments, showed that LSD dissociates exceptionally slowly from both 5-HT2B and 5-HT2A, the receptor central to psychedelic effects.² Simulations attributed the slow kinetics to a lid formed by an extracellular loop over the binding pocket. Loosening that lid by mutation sped LSD’s dissociation and blunted one arm of its signaling.² These slow receptor kinetics provide a molecular basis for effects that last longer than the drug itself stays in the bloodstream.

Location Shapes the Signal

5-HT2A activation alone is not the full story. Serotonin activates the same receptor but does not reproduce the growth-promoting effects of psychedelics. Vargas and colleagues showed that the plasticity-promoting pool of 5-HT2A is intracellular, and serotonin, unlike lipophilic psychedelics, cannot readily cross the membrane to reach it.³ This location bias separates psychedelics from endogenous serotonin at the same receptor.

Not the Only Door

The 5-HT2A receptor is not the only fast route to change. Esketamine, approved for treatment-resistant depression, acts through non-competitive NMDA-receptor antagonism on inhibitory interneurons, disinhibiting glutamate and engaging downstream plasticity pathways.⁴ Two different receptor targets converge on overlapping signaling, underscoring that the receptor engaged, not the overall level of serotonin, defines these approaches.

What It Means for GAD

In GAD, the finding that fits this receptor biology is durability. In a Phase 2b trial of the investigational 5-HT2A agonist DT120 (lysergide) ODT, the single-dose benefit was still evident at week 12, a prespecified secondary timepoint, when 65.0% of patients responded versus 30.8% with placebo (the trial also met its week-4 primary endpoint).⁵ An effect that holds after one dose is consistent with slow 5-HT2A engagement and intracellular signaling, a plausible basis for lasting change that daily reuptake blockade does not. Whether that benefit endures in larger, confirmatory trials is what the ongoing Phase 3 GAD program will show.

References

1. Kim K, Che T, Panova O, et al. Structure of a Hallucinogen-Activated Gq-Coupled 5-HT2A Serotonin Receptor. Cell. 2020;182(6):1574-1588.
2. Wacker D, Wang S, McCorvy JD, et al. Crystal Structure of an LSD-Bound Human Serotonin Receptor. Cell. 2017;168(3):377-389.
3. Vargas MV, Dunlap LE, Dong C, et al. Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors. Science. 2023;379(6633):700-706.
4. van Hoogdalem MW, Fu DJ, Drevets WC, Zannikos PN. Esketamine Nasal Spray: Mechanism of Action, Clinical, and Translational Science. Clin Transl Sci. 2026;19:e70527.
5. Robison R, Barrow R, Conant C, et al. Single Treatment With MM120 (Lysergide) in Generalized Anxiety Disorder: A Randomized Clinical Trial. JAMA. 2025;334(15):1358-1372.

Three targets, one downstream destination: How current and investigational approaches engage the brain, by mechanism

References

1. Kim K, Che T, Panova O, et al. Structure of a Hallucinogen-Activated Gq-Coupled 5-HT2A Serotonin Receptor. Cell. 2020;182(6):1574-1588.
2. Wacker D, Wang S, McCorvy JD, et al. Crystal Structure of an LSD-Bound Human Serotonin Receptor. Cell. 2017;168(3):377-389.
3. Vargas MV, Dunlap LE, Dong C, et al. Psychedelics promote neuroplasticity through the activation of intracellular 5-HT2A receptors. Science. 2023;379(6633):700-706.
4. van Hoogdalem MW, Fu DJ, Drevets WC, Zannikos PN. Esketamine Nasal Spray: Mechanism of Action, Clinical, and Translational Science. Clin Transl Sci. 2026;19:e70527.
5. Robison R, Barrow R, Conant C, et al. Single Treatment With MM120 (Lysergide) in Generalized Anxiety Disorder: A Randomized Clinical Trial. JAMA. 2025;334(15):1358-1372.

From chemistry to wiring

Monoaminergic antidepressants raise synaptic serotonin within hours but take weeks to relieve symptoms, and the response is often partial. Interest in psychedelics stems from a different mechanism of action. Vargas and colleagues showed that psychedelic-induced cortical plasticity depends on activation of 5-HT2A receptors located inside the neuron, not only at the cell surface. This is why compounds lipophilic enough to cross the membrane are able to promote plasticity.¹ That finding shifts the focus from serotonin signaling to the machinery that builds and prunes synapses.

What one dose does to a synapse

The structural effects of psychedelics on synapses are measurable and fast. In preclinical studies, a single dose of psilocybin raised dendritic-spine density in mouse frontal cortex by roughly 10% within a day, and the gain persisted about a month.² The same study also found larger spine heads, stronger excitatory transmission, and reversal of a stress-related behavioral deficit.² A broader review suggests that this kind of plasticity involves mTOR- and AMPAR-linked signaling pathways.³

Why this matters for anxiety

Psychoplastogens, compounds that produce rapid and lasting neural plasticity, do the opposite of chronic stress, which strips dendritic spines from the prefrontal circuits that regulate fear and worry. A study by Moda-Sava and colleagues showed how much those spines matter: in a stress model, the psychoplastogen ketamine produced behavioral effects before new spines formed, but selectively eliminating the new prefrontal spines later abolished the sustained benefit. Spine formation, in other words, maintains recovery rather than triggering it.⁴ Reduced cortical spine density is itself a hallmark of several neuropsychiatric disorders.¹ If the same holds in humans, the persistence of newly formed connections may support lasting symptom improvement in chronic, relapsing conditions such as GAD.

Does the model hold in humans?

Whether these findings will translate into better treatments for GAD remains uncertain. The spine and circuit findings are preclinical, and the link between plasticity and lasting clinical benefit remains a hypothesis. At present, the neuroplasticity model helps explain why single-dose psychedelics are being investigated for GAD. If future research confirms these preclinical findings in humans, it could point toward treatments that produce durable benefit by restoring synaptic connections worn down by chronic stress.

Two Mechanistic Routes Under Study in GAD: Different mechanisms, one goal of lasting relief