New Research Puts NMDA Antagonist Side Effects Under the Microscope
A new clinical review published in Psychiatric Times (April 2026) takes a systematic look at the side effect profiles and discontinuation rates of NMDA receptor antagonists used in treatment-resistant depression (TRD) — the drug class that includes both ketamine and esketamine (Spravato). While the research covers the broader landscape of NMDA-targeting therapies, its findings carry direct relevance for anyone using or considering oral ketamine tablets as part of their depression treatment.
The review synthesizes data across delivery methods and compounds, examining which side effects are most commonly reported, how severe they tend to be, and — critically — how often patients stop treatment because of them. Discontinuation rates are a meaningful real-world metric: they reflect not just tolerability, but whether patients feel a treatment is worth continuing given how it makes them feel.
The Core Findings: Tolerability Varies by Route and Dose
The review's central insight is one that experienced ketamine clinicians have long observed: the side effect burden of NMDA antagonists is highly sensitive to route of administration, peak plasma concentration, and the rate at which drug levels rise in the bloodstream. This is where the oral tablet formulation stands apart from IV infusions and intranasal esketamine in meaningful ways.
Intravenous ketamine delivers drug rapidly into circulation, producing high peak concentrations that are associated with more pronounced dissociative experiences, transient blood pressure elevation, and perceptual disturbances — the effects that most patients think of when they imagine ketamine's psychoactive side effects. Intranasal esketamine (Spravato) follows a different absorption curve but still achieves relatively rapid central nervous system exposure, which is why it requires in-clinic monitoring for two hours post-dose.
Oral ketamine tablets, by contrast, undergo first-pass metabolism in the liver before reaching systemic circulation. This process converts a meaningful portion of the ketamine to norketamine — an active metabolite that contributes to antidepressant effect but with a different, generally milder psychoactive profile. The result is a slower rise to a lower peak concentration. For many patients, this translates to a more tolerable acute side effect window: less intense dissociation, lower risk of nausea, and a reduced likelihood of cardiovascular fluctuation during dosing.
The tradeoff, as the research context makes clear, is that bioavailability is lower and more variable with oral dosing. Patients and prescribers must calibrate dose accordingly, and the therapeutic window requires more individualized titration than IV protocols. That variability also means that some patients may not absorb enough active compound to achieve consistent antidepressant benefit — an important factor when evaluating why a patient might discontinue.
Discontinuation: When Side Effects Outweigh the Benefit
Discontinuation data from NMDA antagonist trials reveals a nuanced picture. Across the reviewed studies, discontinuation due to adverse effects was not negligible — particularly for IV ketamine at higher doses and for esketamine in patients with sensitivity to dissociative effects or nausea. Importantly, the review suggests that many discontinuations occur early in treatment, before therapeutic benefit has had time to accumulate, which underscores the importance of expectation-setting and support during the initial dosing period.
For oral ketamine users, the discontinuation story looks somewhat different. Because side effects are generally milder at equivalent therapeutic doses, patients may be more likely to persist through the early titration phase. However, the review also flags that tolerability is only part of the discontinuation equation — if patients don't perceive benefit, they stop regardless of how well they tolerate the medication. This is a reminder that oral ketamine's gentler side effect profile is an advantage only when the dosing is adequate to produce therapeutic effect.
Practical Implications for Oral Ketamine Tablet Users
For patients currently taking or evaluating oral ketamine tablets, here is what this research landscape reinforces:
- Mild dissociation is expected and manageable. Unlike IV ketamine's more pronounced perceptual effects, oral ketamine typically produces subtle cognitive softening or mild visual changes at therapeutic doses. This is a feature of the route, not a sign that something is wrong. Planning doses for low-demand periods — evenings, days off — reduces functional interference.
- Nausea is less common but not absent. Taking tablets with a small, light meal or snack (not a full stomach, which slows absorption) can reduce GI discomfort without substantially blunting peak drug levels. Ginger supplements or anti-nausea medication can be discussed with your prescriber if this is a recurring issue.
- Blood pressure monitoring remains relevant. Even oral formulations can transiently raise blood pressure. Patients with hypertension or cardiovascular concerns should discuss monitoring protocols with their prescriber, particularly in the early titration phase.
- Mood benefit may take time. Unlike the rapid lift many patients feel during or after an IV infusion, oral ketamine's antidepressant effect often builds over days to weeks. Understanding this timeline helps patients persist through the early period when side effects may be present but benefit hasn't yet arrived.
Key Takeaway
Oral ketamine tablets carry a milder acute side effect profile than IV or intranasal routes — but lower bioavailability means dose calibration is critical. If you're experiencing significant side effects or no benefit at your current dose, talk to your prescriber before stopping. Most discontinuations happen before therapeutic benefit has time to develop.
How Tablets Fit Into the Broader NMDA Antagonist Landscape
The Psychiatric Times review is a useful reminder that ketamine is not a monolithic treatment — it exists in a family of NMDA-targeting therapies, each with distinct pharmacokinetics, side effect profiles, regulatory status, and access logistics. Esketamine nasal spray (Spravato) is FDA-approved for TRD and major depressive disorder with suicidal ideation, requires in-clinic administration, and is covered by many insurance plans — but the clinic visit burden and acute dissociative side effects lead some patients to seek alternatives. IV ketamine is widely used off-label, is highly effective, but requires infusion clinic access, is rarely covered by insurance, and carries higher acute side effect burden at standard doses.
Oral ketamine sits in a distinct niche: it's the most accessible format (home administration under prescriber guidance), has the gentlest acute side effect profile, and for many patients with mild-to-moderate TRD represents a sustainable long-term option. The tradeoff is that clinical evidence is less robust than for IV or esketamine, and the variable bioavailability demands a more engaged prescriber-patient relationship around titration.
As research on NMDA antagonists continues to mature, oral formulations are increasingly part of the clinical conversation. Understanding how tolerability and discontinuation data compares across routes helps patients make informed decisions — and helps them stay in treatment long enough to find out if ketamine can work for them.
Source: Psychiatric Times, April 22, 2026
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