What the Review Found
A newly published review in Psychiatric Times (April 2026) takes stock of where glutamate-targeting treatments stand in the management of treatment-resistant depression (TRD) — a condition affecting roughly 30% of people who try antidepressants. The piece focuses primarily on two approved agents: intranasal esketamine (Spravato) and the combination drug dextromethorphan-bupropion (Auvelity). Both work through the glutamatergic system rather than the traditional monoamine pathways targeted by SSRIs and SNRIs, and both have demonstrated meaningfully faster onset of antidepressant effects in clinical trials.
The review's central argument is mechanistic: when the monoamine system fails to produce adequate antidepressant response, glutamate modulation — particularly through NMDA receptor antagonism — can stimulate synaptogenesis, the growth of new synaptic connections in regions like the prefrontal cortex and hippocampus that are structurally compromised in chronic depression. This neuroplasticity effect is now considered central to why ketamine-class drugs produce rapid symptom relief, sometimes within hours of a single dose, compared to the two-to-six-week lag typical of conventional antidepressants.
The original review is available via Psychiatric Times.
Why This Matters for Low-Dose Ketamine Specifically
Most of the clinical trial data cited in reviews like this one centers on IV ketamine at anesthetic-adjacent doses or on intranasal esketamine, which delivers the S-enantiomer of the ketamine molecule in controlled clinical settings. Low-dose oral or sublingual ketamine — the formats most commonly used in outpatient mental health contexts — operates in a lower concentration range and is not yet the subject of the same volume of controlled trial evidence. That distinction matters when interpreting this research.
That said, the mechanism being described is the same one believed to underlie low-dose ketamine's antidepressant effects. NMDA receptor antagonism at sub-anesthetic doses still triggers downstream AMPA receptor activation and BDNF release, both of which drive the synaptogenesis the review emphasizes. The difference is largely one of intensity and kinetics: lower doses tend to produce subtler, more gradual effects with a more tolerable side effect profile, while higher doses produce faster and more pronounced acute responses alongside greater dissociative effects.
For people using low-dose ketamine for depression — particularly those who have not responded to multiple prior antidepressants — this review reinforces the rationale for why their treatment approach is mechanistically sound. The glutamate pathway is increasingly recognized not as a niche alternative to monoamine-based care, but as a distinct and complementary system with its own therapeutic logic.
How Strong Is the Evidence?
It is worth being precise about what this review does and does not establish. Narrative reviews in psychiatry journals synthesize existing literature — they do not generate new data. The strength of any conclusion drawn from a review depends entirely on the quality and consistency of the underlying trials, and TRD research has historically suffered from heterogeneous patient populations, short follow-up windows, and high placebo response rates.
Esketamine has the most robust regulatory backing of the glutamate-targeting agents, having cleared FDA review for TRD in 2019 with a required Risk Evaluation and Mitigation Strategy (REMS) program due to concerns about dissociation and abuse potential. Longer-term maintenance data for esketamine has continued to accumulate, with studies suggesting that ongoing treatment reduces relapse risk — though the optimal dosing interval and duration remain areas of active investigation. Dextromethorphan-bupropion has a more modest evidence base and works through a partially different mechanism, making direct comparisons with ketamine-class compounds difficult.
For low-dose ketamine users, the honest summary is this: the mechanistic rationale is well-supported, the acute efficacy data for ketamine in TRD is substantial, and the long-term picture is still being filled in. Anyone using ketamine as part of a depression management plan should expect ongoing refinement of dosing and maintenance guidance as that evidence matures.
Key Takeaway for Low-Dose Ketamine Patients
This review reinforces that glutamate-targeting treatments represent a scientifically grounded approach to treatment-resistant depression, not a fringe intervention. However, most of the cited evidence applies to higher-dose IV ketamine or intranasal esketamine — not directly to low-dose oral or sublingual formats. Speak with your prescribing clinician about how the maintenance and monitoring considerations discussed in the TRD literature apply to your specific dose range and treatment schedule. Do not adjust dosing frequency based on general TRD trial data without clinical guidance.
Practical Implications for Ongoing Treatment
A few themes in the glutamate TRD literature have direct relevance for people on low-dose ketamine protocols. First, the question of maintenance: early ketamine research focused heavily on acute response, but the field has shifted toward understanding how to sustain benefits over time. For most patients, single-dose or short-course treatment is insufficient; regular maintenance dosing — whether weekly, biweekly, or monthly — appears necessary to preserve synaptogenesis gains. Your own maintenance schedule should be informed by symptom tracking and clinician assessment, not a fixed calendar.
Second, the review's emphasis on synaptogenesis as the therapeutic mechanism has implications for expectations. Neuroplasticity changes are not instantaneous or permanent — they require reinforcement. This is part of why many clinicians pair ketamine treatment with psychotherapy: behavioral and psychological work may help consolidate the structural changes the drug facilitates. If you are using low-dose ketamine without any adjunctive therapeutic work, it is worth discussing with your provider whether that combination could improve durability of response.
Third, safety monitoring remains relevant. Glutamate-targeting agents as a class carry risks — including dissociation, cardiovascular effects at higher doses, and potential for psychological dependence with unsupervised use. Low-dose protocols are specifically designed to minimize these risks, but they do not eliminate them entirely. Regular check-ins with your prescribing clinician, honest reporting of any unusual cognitive or perceptual effects, and avoiding dose escalation without oversight are all consistent with the cautious, evidence-aligned approach this class of treatment warrants.
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