Glutamate Pathways Are Reshaping TRD Treatment

Why Glutamate Is Now at the Center of Depression Treatment

A review published in Psychiatric Times in April 2026 offers a detailed look at how targeting the glutamatergic system is changing the landscape for patients with treatment-resistant depression (TRD). For decades, antidepressant development focused almost exclusively on monoamine neurotransmitters — serotonin, norepinephrine, and dopamine. But for the roughly one-third of depression patients who don't respond to those approaches, clinicians and researchers have been forced to look elsewhere.

The glutamate system — and specifically the NMDA receptor — has emerged as the most promising alternative target. Two drugs are now at the forefront of this shift: esketamine (Spravato), the FDA-approved nasal spray derived from ketamine, and dextromethorphan-bupropion (Auvelity), an oral combination that also modulates NMDA receptors. Both work through mechanisms that go beyond symptom suppression, actually promoting synaptogenesis — the formation of new synaptic connections — which may explain why patients often report relief within hours rather than weeks.

Where Ketamine Troches Fit in This Evolving Picture

The review focuses primarily on esketamine and dextromethorphan-bupropion because they hold FDA approval, but the underlying science it describes applies directly to compounded ketamine troches — the at-home, sublingual format that many TRD patients are already using through telehealth-based prescribing programs.

Ketamine troches work through the same core mechanism: NMDA receptor antagonism that triggers a downstream glutamate surge, activating AMPA receptors and promoting BDNF (brain-derived neurotrophic factor) release. That cascade is what drives the rapid antidepressant effect and the neuroplasticity changes the review highlights. In practical terms, this means troches aren't simply a delivery workaround — they're tapping into the same pharmacological pathway that has made esketamine a clinical breakthrough.

The key differences are in delivery and context. Esketamine must be administered in a certified healthcare setting with two hours of post-dose monitoring. Ketamine troches, by contrast, are dissolved sublingually at home, typically over 15–20 minutes, with absorption occurring through the oral mucosa before the remainder is swallowed. This produces a more gradual plasma curve compared to IV infusion or nasal spray, which translates to a gentler dissociative experience for most patients — a meaningful consideration for those who find clinic-based dosing logistically difficult or anxiety-inducing.

Dextromethorphan-bupropion (Auvelity) is worth noting as a distinct option: it's oral, taken daily, and carries a milder dissociative profile. For patients who want a glutamate-targeting option without any psychedelic component, it may become a more common bridge or alternative. But its onset and depth of effect appear more modest compared to ketamine-based treatments in the early data.

What This Means for Your Troche Protocol in Practice

For patients already on a troche regimen, the review reinforces several practical points worth discussing with your prescribing clinician:

• Dosing frequency matters for neuroplasticity. The synaptogenesis effects described in the research are not permanent after a single dose — they require repeated activation to sustain structural changes. Most troche protocols involve doses two to three times per week during an induction phase, then taper to maintenance. If you've been inconsistent with your schedule, this science underscores why regularity supports better outcomes.
• The dissociative window is part of the mechanism. Some patients try to minimize the psychoactive experience by using very low troche doses. While that may reduce side effects, it can also blunt the NMDA antagonism needed to trigger the glutamate cascade. Work with your provider to find a dose that balances tolerability with therapeutic effect.
• Troches remain compounded — and that matters for access. Unlike esketamine, ketamine troches are not FDA-approved products. They are compounded by licensed pharmacies under a prescription. This means their availability is tied to compounding pharmacy regulations and prescriber willingness, not a manufacturer's distribution network. The growing clinical validation of glutamate-based approaches may increase prescriber confidence — but patients should stay informed about any regulatory changes affecting compounding access.
• Combination approaches are gaining attention. The review notes that combining glutamate-targeting agents with existing antidepressants is an area of active study. If you're on an SSRI or SNRI alongside troches, that combination is increasingly supported by emerging practice patterns — though your prescriber should always guide any changes to your full medication stack.

The broader takeaway from this 2026 review is that ketamine-based treatment is no longer on the fringe of psychiatric care. The glutamatergic pathway is now a primary therapeutic target, and troches represent one of the most accessible entry points into that treatment category for patients who can't or won't use clinic-based infusions or nasal spray. As the evidence base grows, expect more nuanced protocols — and more prescriber familiarity — to follow.

Source: Psychiatric Times, April 2026