What works for whom? The evidence points to specific drugs, not a blanket answer.
The question of NMDA-modulating antidepressant combinations is really about two different drug classes: the newer dextromethorphan/bupropion combination and the older antipsychotics like brexpiprazole. The most direct answer comes from the pharmacology review, which states that dextromethorphan/bupropion is the first non-antipsychotic FDA-approved for agitation in Alzheimer's dementia, and it works by blocking NMDA receptors and enhancing the antidepressant's effect [5]. This is a strong signal that the approach can work, but the review doesn't provide efficacy numbers, so we can't quantify how well it works from these papers.
For brexpiprazole, the evidence is more concrete. In a pooled analysis of two phase 3 trials, brexpiprazole (2 or 3 mg/day) improved agitation scores significantly more than placebo, but the effect was much larger in people also taking an antidepressant: a 12.1-point greater improvement on the Cohen-Mansfield Agitation Inventory (CMAI) compared to a 2.93-point improvement without an antidepressant [1]. This suggests that combining an antipsychotic with an antidepressant may boost the effect, but it's important to note that the antidepressant in those cases was likely a standard SSRI, not an NMDA modulator.
So, the answer is nuanced: the NMDA-modulating combination (dextromethorphan/bupropion) is approved and likely helps, but the strongest quantitative evidence here is for brexpiprazole, which works better when an antidepressant is already on board. The takeaway is that 'NMDA-modulating antidepressant combinations' is not a single treatment—it's a class of approaches with varying evidence.
The catch: safety concerns and mixed evidence mean it's not a first-line for everyone.
While the efficacy data is promising, safety is a major consideration, especially in older adults with dementia. The dextromethorphan/bupropion review lists several serious risks, including seizures, serotonin syndrome, and a newly added warning about hyponatremia (low sodium), which can mimic dementia progression in the elderly [5]. This means that while it can help, it requires careful monitoring and is contraindicated in people with seizure disorders or eating disorders.
The evidence is also not uniformly positive. The escitalopram trial (S-CitAD), which is an SSRI, not an NMDA modulator, is still ongoing, and its results are not yet available [3]. This is a reminder that not all antidepressants have proven efficacy for agitation. Additionally, a 2024 review of future strategies for Alzheimer's behavioral symptoms notes that conventional treatments are often ineffective, highlighting the need for new therapies [4]. This suggests that while NMDA-modulating combinations are a step forward, they are not a guaranteed solution for every patient.
In the brexpiprazole analysis, the only adverse event that occurred in more than 5% of patients was falls, which happened at a similar rate in the placebo group (6.5% vs. 5.7%) [1]. This is reassuring, but it underscores that falls are a common risk in this population, regardless of treatment.
What to ask your doctor: Is this the right approach for your loved one?
If you're considering an NMDA-modulating antidepressant combination for agitation in Alzheimer's, the first step is to have a detailed conversation with the prescribing doctor. Ask specifically about dextromethorphan/bupropion, since it's the only FDA-approved non-antipsychotic for this indication, and discuss the titration schedule (starting at 30/105 mg once daily, then increasing) and potential side effects like hyponatremia [5].
Also, ask about the evidence for other options. The brexpiprazole data suggests that adding an antidepressant to an antipsychotic might enhance the effect, but this was a post hoc analysis, not a prospective trial, so it should be interpreted cautiously [1]. The doctor can help weigh the risks and benefits based on the patient's specific health profile, including any history of seizures, heart problems, or falls.
Finally, remember that non-drug approaches are often recommended first. The escitalopram trial included a psychosocial intervention before randomization, and participants only received the drug if they didn't respond to that [3]. This highlights that medication is not the only tool, and a comprehensive approach is often best.
About These Sources
This answer is built on 5 peer-reviewed studies — published from 2023 to 2026, 4 from 2024 or later, 4 in Q1 journals, collectively cited 114 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 58 papers retrieved from a database of over 500 million.
Sources used in this answer
Brexpiprazole With Antidepressants for Agitation in Alzheimer’s Dementia: Post Hoc Analysis
In a pooled post hoc analysis of two phase 3 trials, brexpiprazole (2 or 3 mg/day) improved agitation significantly more than placebo, with a much larger effect in those also taking antidepressants (12.1-point greater improvement on CMAI vs. 2.93-point without), and falls were the only common adverse event.
Brexpiprazole for the Treatment of Agitation in Alzheimer Dementia
In a 12-week randomized controlled trial of 345 patients, brexpiprazole (2 or 3 mg/day) led to a statistically significant improvement in agitation (5.32-point greater reduction on CMAI vs. placebo), with good tolerability and low discontinuation rates.
Escitalopram for Agitation in Alzheimer’s Dementia
The S-CitAD trial, a phase 3 randomized placebo-controlled trial of escitalopram (an SSRI) for agitation in Alzheimer's, is ongoing with results expected in 2024, and its outcomes will have major clinical impact regardless of direction.
Future Therapeutic Strategies for Alzheimer’s Disease: Focus on Behavioral and Psychological Symptoms
A 2024 review of behavioral and psychological symptoms in Alzheimer's notes that conventional treatments are often ineffective, and highlights the need for new therapies targeting specific symptoms, including NMDA-related mechanisms.
Dextromethorphan/Bupropion: Pharmacology, Indications, Dosing Guidelines and Adverse Effects
A pharmacology review describes dextromethorphan/bupropion as an oral NMDA receptor antagonist and sigma-1 agonist, FDA-approved for Alzheimer's agitation, with a slower titration schedule for that indication and significant safety warnings including seizures and hyponatremia.