RESEARCH MONOGRAPH · KDC-MN-374

D-Serine

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 3 min read

Our opinion on this compound

67/100

Endogenous NMDA co-agonist with real schizophrenia signal; underappreciated outside the Hashimoto group

Look, D-serine is one of those compounds where the textbook stops being interesting and the real story starts. It's not just a free amino acid sitting in your serum. It's a co-agonist at the glycine-B site of NMDA receptors, and in the forebrain it actually outcompetes glycine for that role. Serine racemase makes it from L-serine. D-amino acid oxidase (DAAO) degrades it. That whole axis has been the schizophrenia hypothesis playground for two decades now.

What we like: the negative-symptom signal in schizophrenia is real but underpowered. Hashimoto, Heresco-Levy, and the Tsai group have run small RCTs in the 30 to 120 mg/kg range showing modest but reproducible improvement in negative and cognitive symptoms when added to standard antipsychotics. Not curative. Not nothing. The follow-up DAAO-inhibitor trials (luvadaxistat from Neurocrine) basically validated the upstream pharmacology even though the phase 2 missed primary.

Sourcing is the catch. D-serine is cheap to make as a free amino acid but the enantiomeric purity matters a lot. L-serine contamination above a couple percent muddies any racemase or NMDA experiment you're trying to run. Chiral HPLC or optical rotation checks should be in the COA, and honestly a lot of suppliers skip that. We do not.

The other thing people miss is renal load. D-serine clears renally and at high preclinical doses it's nephrotoxic in rats. That's a real ceiling on the translational story and probably why everyone shifted to DAAO inhibitors and partial agonists like sarcosine and bitopertin instead of just dumping D-serine into people.

Mechanism-wise it's also showing up in long-term potentiation work, hippocampal plasticity, and a small but interesting line on motor neuron disease (ALS spinal cord has elevated D-serine and serine racemase, which is weird and probably matters). The serine racemase knockout mouse has a memory phenotype that's hard to argue with.

For research use it's a clean tool compound to probe glycine-site occupancy. Just dont treat it like a benign amino acid; it isnt. The kidney signal is the thing to design around.

Evidence: 60
Mechanism: 82
Reliability: 62
Safety: 58
Sourcing: 72
Value: 70
Signal: 65
Staying power: 70

Plain-language summary Intrigue 68 / 100

D-serine is the mirror-image form of the amino acid serine, and your brain makes it on purpose. It is the obligate co-agonist at the synaptic NMDA receptor, meaning the receptor will not open without it sitting in a dedicated pocket alongside glutamate. An enzyme called serine racemase builds it; another called DAAO breaks it down. Researchers have tested giving it as a drug to boost NMDA function in schizophrenia (where reduced NMDA signaling is implicated in negative and cognitive symptoms) and in depression. Phase 2 trials show small but real effects. The competing strategy is to inhibit DAAO so the brain keeps more of its own. The canonical NMDA glycine-site co-agonist for neuroscience research. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Endogenous NMDA receptor co-agonist

D-stereoisomer of serine; an endogenous obligatory co-agonist at the NMDA receptor glycine site.

Abstract

D-serine ((R)-2-amino-3-hydroxypropanoic acid; CAS 312-84-5; molecular formula C3H7NO3; molecular weight 105.09) is the D-stereoisomer of serine, an endogenous obligatory co-agonist at the glycine site of NMDA receptors. The compound is biosynthesized in the brain by serine racemase (the enzyme that converts L-serine to D-serine) and is metabolized by D-amino acid oxidase (DAAO). D-serine is the principal endogenous co-agonist for synaptic NMDA receptors in the cortex and hippocampus, while glycine itself co-agonizes extrasynaptic NMDA receptors. Pharmacologically, exogenous D-serine elevates NMDA receptor function, with research interest in schizophrenia (where reduced NMDA function is hypothesized as a contributor to negative symptoms and cognitive deficits) and depression (NMDA modulation as antidepressant target). Phase 2 trials in schizophrenia have shown small effects. Plasma half-life is approximately 4 hours; oral bioavailability is moderate. The DAAO inhibitor approach is an alternative to direct D-serine administration. Used as the canonical NMDA glycine-site co-agonist in research.

Mechanism of action

Endogenous NMDA receptor glycine-site co-agonist; obligatory for synaptic NMDA receptor activation. Biosynthesized by serine racemase; degraded by DAAO.

Reported research dose ranges

Clinical trials 30 to 120 mg/kg in the published literature; supplement 1 to 4 g.

References

Mothet JP, et al. D-serine is an endogenous ligand for the glycine site of the N-methyl-D-aspartate receptor. Proc Natl Acad Sci 2000.
Tsai G, et al. D-serine added to antipsychotics for the treatment of schizophrenia. Biol Psychiatry 1998.
Wolosker H. D-serine regulation of NMDA receptor activity. Sci Signal 2006.

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KDC-MN-374

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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D-Serine

Abstract

Mechanism of action

Reported research dose ranges

References

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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