Glutamate Pathway Drugs Are Reshaping TRD Care

When Antidepressants Fail, the Brain's Glutamate System Steps In

A new review published in Psychiatric Times in April 2026 takes a close look at how glutamate-targeting medications are changing the landscape for patients with treatment-resistant depression (TRD) — a condition affecting roughly one-third of people diagnosed with major depressive disorder who don't respond adequately to traditional antidepressants.

The piece focuses primarily on two approved agents: esketamine (Spravato), administered intranasally in clinical settings, and the combination drug dextromethorphan-bupropion (Auvelity), taken orally. But for readers tracking oral ketamine specifically, the underlying science applies directly. All of these treatments work through the same general mechanism — blocking NMDA receptors in the brain's glutamate system — and the review offers a useful primer on why that mechanism produces faster, more durable antidepressant effects than monoamine-based drugs like SSRIs and SNRIs.

The core finding: glutamate-modulating drugs appear to rapidly stimulate synaptogenesis — the growth of new synaptic connections in the prefrontal cortex — which may explain why patients often report mood improvement within hours to days rather than the weeks typical of conventional antidepressants.

What the Glutamate Mechanism Means for Oral Ketamine Users

Ketamine's antidepressant action runs through this same glutamate pathway. Whether delivered via IV infusion, nasal spray, sublingual troche, or oral tablet, ketamine and its S-enantiomer esketamine both bind NMDA receptors and trigger downstream signaling cascades — including activation of AMPA receptors and BDNF release — that promote rapid synaptic repair in brain regions implicated in depression.

The distinction between delivery methods matters here. IV ketamine delivers close to 100% bioavailability directly into the bloodstream, producing fast and predictable plasma concentrations. Esketamine nasal spray achieves roughly 40–50% bioavailability through the nasal mucosa. Oral ketamine tablets, by contrast, face significant first-pass metabolism in the liver, yielding bioavailability estimates typically in the 20–30% range — though this varies considerably between individuals based on CYP enzyme activity, gut transit time, and whether the tablet is taken with food.

This lower and more variable bioavailability doesn't make oral tablets less legitimate as a treatment option — it simply means dosing strategies must account for it. Providers prescribing oral ketamine generally start at higher milligram doses than they would for sublingual or IV routes, and titrate carefully to balance therapeutic effect against dissociative side effects. The slower absorption curve of a tablet compared to an IV push also tends to produce a gentler onset, which many patients find more tolerable.

The Psychiatric Times review doesn't address oral tablets directly, but its framing of the glutamate pathway as the primary mechanism of action reinforces that the antidepressant benefit patients seek from ketamine tablets is pharmacologically grounded — not incidental.

How Oral Tablets Fit Into the Broader TRD Treatment Picture

One of the more useful contributions of the Psychiatric Times piece is contextualizing glutamate-based treatments within the stepwise logic of TRD management. Most patients reach TRD status after failing two or more adequate antidepressant trials. At that point, clinicians are increasingly looking beyond monoamine pharmacology — and glutamate-targeting options are now considered a clinically validated next step rather than a last resort.

For patients who want access to ketamine outside of an infusion clinic — either for cost reasons, geographic constraints, or personal preference — oral tablets represent a meaningful option. Infusions remain the gold standard in terms of speed and bioavailability, but they require in-clinic visits, often cost $400–$800 per session, and aren't covered by most insurance plans. Esketamine nasal spray (Spravato) has FDA approval for TRD and some insurance coverage, but requires administration under clinical supervision.

Oral ketamine tablets, typically prescribed through telehealth platforms or psychiatry practices with ketamine programs, offer greater flexibility. Patients can take them at home on a schedule their provider defines, which lowers logistical friction and can support more consistent treatment adherence. The tradeoff is the bioavailability gap and the need for disciplined self-monitoring — patients using tablets at home don't have a clinician in the room to assess dissociative effects in real time.

The growing body of research on glutamate-pathway treatments — including the kind of mechanistic clarity offered in this Psychiatric Times review — continues to build the scientific case for ketamine across its various formulations. As prescribers become more comfortable with the mechanism and the evidence base, access to oral ketamine is likely to expand further, particularly through supervised at-home models with structured check-ins.

Read the original review at Psychiatric Times.