NMDA Antagonist Side Effects: What the Data Says

What the Research Covers

A new clinical analysis published in Psychiatric Times (April 2026) takes a direct look at the side effect profiles and discontinuation rates associated with NMDA receptor antagonists—primarily intravenous ketamine and intranasal esketamine (Spravato)—in patients with treatment-resistant depression (TRD). The piece synthesizes what clinicians are observing in practice and calls for a more systematic, data-driven approach to managing these medications: optimizing doses earlier, switching agents when response stalls, and using structured tools like the PHQ-9 to track progress and tolerability over time.

For readers researching low-dose ketamine as a long-term option, this analysis is worth unpacking carefully—because the side effect picture looks meaningfully different depending on dose, administration route, and how closely patients are monitored.

The Side Effect Landscape for NMDA Antagonists

NMDA receptor antagonists work by temporarily blocking glutamate receptors in the brain, producing rapid antidepressant effects in many patients who haven't responded to standard treatments. But that mechanism also drives a predictable set of short-term side effects. The most commonly reported include dissociation (a feeling of detachment from self or surroundings), dizziness, nausea, elevated blood pressure, and perceptual disturbances such as visual or auditory changes. For IV ketamine, these effects typically peak during or shortly after infusion and resolve within one to two hours. For intranasal esketamine, the dissociative window is similar but monitored under clinical supervision per FDA protocol.

Critically, the Psychiatric Times analysis emphasizes that the severity and frequency of these side effects are not fixed—they respond to dose adjustments. Patients experiencing significant dissociation or blood pressure spikes at standard doses may tolerate lower doses better, often without losing the antidepressant benefit. This is an underappreciated flexibility in the clinical toolkit, and it's directly relevant to the low-dose ketamine model, where intentionally conservative dosing is already standard practice.

Longer-term concerns—including potential impacts on bladder health (more associated with heavy recreational use than clinical protocols), cognitive function, and dependency risk—are acknowledged in the analysis, though the authors note that clinical-use data at therapeutic doses remains reassuring compared to abuse-pattern data. Monitoring remains important, but the risk profile at controlled low doses is substantially different from what recreational misuse literature describes.

Who Is Stopping Treatment—and Why

Discontinuation is a meaningful problem in TRD treatment broadly, and NMDA antagonists are no exception. The analysis identifies several reasons patients stop: intolerable acute side effects (particularly dissociation or anxiety during sessions), inadequate response after an initial series, logistical burden of clinic-based administration, and cost. For esketamine specifically, the requirement for in-office administration and a two-hour post-dose observation window creates real-world friction that contributes to dropout.

What the clinicians behind this analysis argue—and this is the actionable core of the piece—is that many discontinuations are premature or preventable. Patients who stop after two or three sessions because of side effects may not have been given the chance to try a lower dose or a modified protocol. Patients who stop due to perceived non-response may not have been tracked with structured tools (like serial PHQ-9 scores) that could reveal partial or delayed improvement. The recommendation is clear: move faster on dose optimization, don't wait through multiple failed sessions at a suboptimal dose, and use validated scales to make response decisions based on data rather than impression.

What This Means for Low-Dose Ketamine Specifically

The low-dose ketamine model—typically sub-anesthetic IV infusions in the 0.3–0.5 mg/kg range, or oral/sublingual formulations at even lower equivalent doses—is in many ways a direct response to the tolerability challenges this analysis describes. By keeping plasma concentrations lower, the intensity of dissociation and hemodynamic changes is reduced, often substantially. Many patients in low-dose protocols report minimal or no perceptual side effects, which changes the discontinuation calculus significantly.

That said, this research reinforces a few principles that apply regardless of dose level. First, response tracking matters. Whether you're receiving infusions, lozenges, or nasal spray, using a standardized depression scale before and after treatment cycles gives you and your provider real data on whether the intervention is working—and when it might be time to reassess. Second, side effect communication should be proactive. Clinicians optimizing doses need accurate reports from patients; tolerating significant side effects silently doesn't serve anyone. Third, patience with the protocol has limits. The analysis explicitly discourages indefinitely continuing a dose or regimen that isn't producing measurable improvement. Switching formulations or adjusting frequency should happen on a defined timeline, not indefinitely.

For patients on maintenance low-dose ketamine—those using periodic sessions to sustain remission rather than achieve initial response—the discontinuation data is a reminder that long-term adherence is itself a clinical outcome worth managing. Simplifying administration (home-based oral or sublingual options where appropriate), minimizing side effects through conservative dosing, and maintaining regular outcome monitoring all support sustained benefit over time.

How Strong Is the Evidence?

This Psychiatric Times piece is a clinical commentary and synthesis rather than a new randomized trial, so it should be read as expert interpretation of existing data rather than primary evidence. The underlying side effect and discontinuation data it draws from varies in quality—some from rigorous RCTs, some from observational registry studies and real-world clinical reports. The call for faster dose optimization and structured outcome tracking is evidence-informed but also reflects emerging clinical consensus rather than settled protocol. Clinicians will apply these recommendations differently depending on their practice context and patient population.

For patients, this is a useful framework for conversations with providers, not a directive to self-adjust treatment. The core message—that side effects are manageable, discontinuation is often avoidable with the right adjustments, and data-driven tracking improves outcomes—is well-grounded and practical regardless of the evidence grade behind any specific recommendation.

Source: Psychiatric Times, April 22, 2026