A handful of supplements show early promise as add-ons to standard OCD treatment, but none have enough evidence to stand on their own as primary therapy. N-acetylcysteine (NAC), inositol, zinc, and a few herbal extracts have performed well in small trials, mostly when paired with an SSRI or another first-line medication. The research is genuinely interesting, and some of it is more rigorous than you might expect, but the honest picture is that most supplements for OCD have been tested in only one or two controlled trials with small sample sizes.
N-Acetylcysteine (NAC)
NAC is probably the most studied supplement for OCD, and the results are encouraging enough that some psychiatrists already recommend it informally. NAC is an amino acid derivative that your body converts into glutathione, a major antioxidant. In the brain, it also modulates glutamate, a neurotransmitter increasingly linked to OCD. Glutamate dysfunction in circuits connecting the cortex, striatum, and thalamus is one of the leading theories for what goes wrong in the condition.1PubMed Central. Glutamatergic Synaptic Dysfunction and Obsessive-Compulsive Disorder NAC may help by normalizing glutamate levels in those circuits.
In a multicenter randomized trial of children and adolescents with OCD already taking citalopram (an SSRI), adding NAC dropped symptom scores substantially. The NAC group’s average score on the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), the standard measure, fell from about 21 to about 11 over the study period, with a large effect size. The placebo group did not see a meaningful change.2PubMed Central. Efficacy of N-Acetylcysteine Augmentation on Obsessive Compulsive Disorder: A Multicenter Randomized Double Blind Placebo Controlled Clinical Trial The supplement was also well tolerated, which matters when you are talking about adding something to an existing medication regimen. Typical doses in OCD studies range from about 600 mg to 2,400 mg daily, usually divided into two doses.
NAC is available cheaply over the counter and has a fairly benign side-effect profile at the doses used in psychiatric research. Nausea and mild gastrointestinal discomfort are the most common complaints. Still, its role is as an adjunct. No trial has tested it as a standalone replacement for SSRIs or cognitive behavioral therapy in OCD.
Inositol
Inositol is a sugar alcohol involved in how brain cells relay signals from serotonin receptors. Because SSRIs work by boosting serotonin signaling and inositol plays a role in the same downstream pathway, researchers tested whether supplementing it might ease OCD symptoms. In a small double-blind crossover trial, 13 patients took 18 grams of inositol daily for six weeks and placebo for six weeks. Inositol significantly reduced OCD symptom scores compared with placebo.3PubMed. Controlled trials of inositol in psychiatry
The dose used in that trial, 18 grams a day, is worth noting. That is a heaping tablespoon of powder, far more than you would get from any typical diet. At those quantities, inositol can cause bloating, gas, and loose stools. It is generally considered safe, but the required dose is high enough that many people find it inconvenient or unpleasant. Inositol has also shown benefits in other anxiety-related conditions like panic disorder, which makes its effect on OCD plausible rather than a fluke, though replication studies in OCD specifically are still limited.
Zinc as an SSRI Booster
Zinc plays a role in neurotransmitter function and has anti-inflammatory and antioxidant properties in the brain. In a randomized placebo-controlled trial, patients already taking fluoxetine (Prozac) were given either zinc sulfate or placebo as an add-on. Both groups improved, but the zinc group had significantly lower Y-BOCS scores at weeks 2 and 8 compared to the fluoxetine-plus-placebo group.4PubMed. Evaluation of oral zinc sulfate effect on obsessive-compulsive disorder: a randomized placebo-controlled clinical trial That is a narrow evidence base, a single study, but the design was solid and the results were in the right direction.
Zinc supplementation at standard doses (around 220 mg zinc sulfate daily, which delivers roughly 50 mg of elemental zinc) is generally safe for most adults for short periods. Long-term high-dose zinc can interfere with copper absorption, so if you are supplementing zinc for more than a few weeks, periodic copper monitoring or a small copper supplement is a reasonable precaution.
Saffron and Milk Thistle
Two herbal supplements have been tested head-to-head against standard SSRI medications rather than as add-ons, and the results are intriguing if preliminary. In a double-blind trial comparing saffron extract (30 mg daily) to fluvoxamine in patients with mild to moderate OCD, both groups improved at similar rates over the trial period, with no statistically significant difference between them.5PubMed Central. Comparison of Saffron and Fluvoxamine in the Treatment of Mild to Moderate Obsessive-Compulsive Disorder: A Double Blind Randomized Clinical Trial A separate trial compared crocin, the active pigment in saffron, to fluoxetine and found comparable OCD symptom improvement, with fewer side effects in the crocin group.6PubMed. Effect of crocin versus fluoxetine in treatment of mild to moderate obsessive-compulsive disorder: A double blind randomized clinical trial
Milk thistle, which contains the flavonoid complex silymarin, was tested in a similar way. A small randomized trial of 35 patients found no significant difference in OCD symptom reduction between milk thistle at 600 mg per day and fluoxetine. The herbal extract’s positive effects appeared to kick in around the fifth week, with milder side effects than the SSRI.7PubMed Central. Nutritional and herbal supplements in the treatment of obsessive compulsive disorder
These “non-inferiority” results sound impressive, but they come with a major caveat. When a trial compares a supplement to a drug and finds “no significant difference,” it does not necessarily mean the supplement works as well as the drug. It can also mean the study was too small to detect a real difference. With only 35 to 50 patients in these trials, the statistical power to detect a moderate gap is limited. The results are worth exploring further, but they are not strong enough to justify swapping out a medication that is working for you.
Vitamin D and B12 Deficiencies
Several studies have found that people with OCD tend to have lower vitamin D levels than matched controls. In one study, vitamin D levels in the OCD group were significantly lower, and the number of participants with deficiency or insufficiency was markedly higher than in the control group. More telling, vitamin D levels were inversely correlated with symptom severity: lower vitamin D, worse obsessions and compulsions.8PubMed Central. Investıgation of vitamin D levels in obsessive-compulsive disorder Similar patterns have been found in younger populations, with children and adolescents with OCD showing significantly lower vitamin B12 and vitamin D levels and higher homocysteine compared to controls.9Psychiatry Research. Vitamin B12, folic acid, homocysteine and vitamin D levels in children and adolescents with obsessive compulsive disorder
The catch is that correlation is not causation. People with OCD might spend more time indoors (less sun exposure), eat less varied diets, or have underlying biological differences that happen to affect both vitamin D and brain function. That said, correcting a genuine deficiency is worthwhile regardless of whether it directly improves OCD symptoms. Vitamin D supports immune function, bone health, and mood regulation through multiple pathways. One proposed mechanism specific to OCD is that vitamin D stimulates glutathione production in the brain, which ties it back to the same antioxidant system that NAC targets.10PubMed. N-Acetyl Cysteine and Vitamin D Supplementation in Treatment Resistant Obsessive-compulsive Disorder Patients: A General Review If your levels are low, supplementing makes sense on general health grounds, with the potential OCD benefit as a bonus.
Glycine and the Glutamate Connection
Glycine is an amino acid that acts as a co-activator at NMDA receptors, which are part of the brain’s glutamate signaling system. Because glutamate dysfunction in circuits connecting the cortex, striatum, and thalamus is implicated in OCD,11Journal of Mood & Anxiety Disorders. Reconsidering the glutamate hypothesis of obsessive-compulsive disorder: A systematic review of proton magnetic resonance spectroscopy studies in unmedicated participants researchers have been interested in whether modulating NMDA receptors could help.
The evidence for glycine is thin but suggestive. A case report described one patient who took high-dose glycine over five years and experienced robust reduction in OCD and body dysmorphic disorder symptoms, with partial relapses when treatment was paused.12PubMed Central. High-dose glycine treatment of refractory obsessive-compulsive disorder and body dysmorphic disorder in a 5-year period A small placebo-controlled trial in 14 adults found that those receiving glycine had a larger average drop in Y-BOCS scores than placebo (about 6 points versus 1 point), but the difference did not quite reach statistical significance.13PubMed. Adjunctive glycine in the treatment of obsessive-compulsive disorder in adults The doses used in these studies were very high, often 60 grams per day, which is impractical for most people and can cause significant gastrointestinal side effects. Glycine is more of a research curiosity at this point than a practical supplement option.
Ashwagandha
Ashwagandha (Withania somnifera) is an adaptogenic herb widely used in Ayurvedic medicine. It has anti-anxiety properties attributed to its effects on GABA receptors, cortisol modulation, and antioxidant activity. A review of clinical evidence found that ashwagandha modestly benefits OCD alongside generalized anxiety disorder and several other neuropsychiatric conditions.14PubMed. Potential clinical applications of Ashwagandha (Withania somnifera) in medicine and neuropsychiatry
The word “modestly” is doing heavy lifting there. The OCD-specific data for ashwagandha is sparse compared to its anxiety data. If you already take ashwagandha for general anxiety or stress and also have OCD, there may be some spillover benefit. But the evidence does not support choosing ashwagandha specifically to target OCD symptoms when supplements with more direct trial data, like NAC, are available.
What Has Not Worked
Not every supplement that seems plausible on paper performs in practice. Omega-3 fatty acids, specifically EPA (eicosapentaenoic acid), looked like a reasonable candidate given their anti-inflammatory properties and benefits in depression research. But a placebo-controlled crossover trial found that adjunctive EPA was ineffective against OCD. Y-BOCS scores dropped similarly in both the EPA and placebo phases, suggesting the improvement was just a time effect rather than a treatment effect.15ScienceDirect / Journal of Psychiatric Research. A placebo-controlled cross-over trial of adjunctive EPA in OCD This is a useful reminder that positive effects in depression or general anxiety do not automatically translate to OCD, which has its own distinct neurobiology.
The Gut-Brain Angle
Probiotic supplements are generating excitement across psychiatry, and OCD research is no exception. In a rat model, eight weeks of multistrain probiotic treatment abolished compulsive and anxiety-like behaviors that had been induced by a drug. The treatment also reshaped the animals’ gut microbiome, increasing certain species of Bifidobacterium while decreasing specific Lactobacillus strains.16PubMed. Multistrain probiotic rescinds quinpirole-induced obsessive-compulsive disorder phenotypes by reshaping of microbiota gut-brain axis in rats
This is animal data, and animal models of OCD are rough approximations at best. A rat performing repetitive checking behavior after being given a dopamine agonist is not the same thing as a person locked in an intrusive thought loop about contamination. The biological plausibility is there: the gut produces neurotransmitters, gut bacteria influence inflammation, and inflammation has been linked to OCD progression.17Springer Nature. Targeting inflammatory signaling in obsessive compulsive disorder: a promising approach But until controlled trials in humans are published, probiotics for OCD remain speculative. Taking a general probiotic for digestive health is unlikely to hurt, but do not expect it to meaningfully move the needle on compulsions.
How Good Is the Evidence Overall?
A systematic review that assessed the quality of complementary medicine studies in OCD found that the nutraceutical studies (supplements and herbal medicines) actually scored well on methodological quality, averaging about 8.6 out of 10.18PubMed. Complementary medicine, self-help, and lifestyle interventions for obsessive compulsive disorder (OCD) and the OCD spectrum: a systematic review The problem is not sloppy design so much as small scale. Most of these trials enrolled between 14 and 50 participants. A well-designed study of 35 people can tell you a supplement is worth investigating further, but it cannot tell you with confidence how large the real effect is or who will benefit most.
A recent narrative review looking across multiple supplement categories concluded that certain nutritional interventions appear to offer safe, well-tolerated adjunctive benefits in OCD, likely through anti-inflammatory and antioxidant pathways.19PubMed. The Therapeutic Effects of Dietary Supplements on OCD: A Narrative Review Consistent differences in glutamate, homocysteine, vitamin B12, vitamin E, and zinc levels between people with OCD and healthy controls suggest these nutrients are not random targets but may be tied to real biological mechanisms driving symptoms.
The practical takeaway: if you are already on an SSRI and doing exposure-response prevention therapy (the gold standard for OCD), asking your doctor about adding NAC, correcting a vitamin D deficiency, or trying inositol is reasonable. These supplements have the most human evidence. If you are not yet on first-line treatment, that is where to start. No supplement has enough evidence to replace SSRIs or therapy, and treating OCD with supplements alone would mean choosing the least-proven option for a condition where effective treatments already exist.
Interactions Worth Knowing About
Most supplements discussed here are well tolerated at the doses used in research, but interactions with OCD medications deserve attention. NAC can affect the absorption of certain drugs if taken at the same time. Inositol at high doses can cause GI distress that mimics SSRI side effects, making it harder to tell which one is responsible if problems develop. Zinc competes with copper for absorption, and long-term high-dose zinc can cause copper deficiency, which brings its own neurological risks. Saffron at very high doses has blood-thinning properties, which matters if you are on any anticoagulant. Ashwagandha may potentiate the sedating effects of benzodiazepines or other calming medications sometimes prescribed alongside SSRIs for OCD.
Perhaps the biggest practical concern is serotonin syndrome risk. SSRIs raise serotonin levels, and several supplements, including inositol and St. John’s Wort (which was not discussed here because it has not been well-studied for OCD specifically), also affect serotonin pathways. Combining multiple serotonin-active substances without medical oversight can, in rare cases, produce a dangerous excess. If you are taking an SSRI for OCD and want to add any supplement, run it by your prescriber first. This is not a formality; it is genuine risk management for a small but real danger.
Creatine and Other Emerging Targets
Creatine monohydrate, better known in the fitness world, is drawing early attention in psychiatric research. The brain is a major consumer of creatine for energy metabolism, and impairments in creatine metabolism have been linked to several brain disorders.20PubMed Central. Creatine metabolism and psychiatric disorders: Does creatine supplementation have therapeutic value? Depression research with creatine has progressed further than OCD research, but the theoretical rationale for exploring it in OCD exists. No controlled OCD-specific trial of creatine has been published yet, so this remains a watch-this-space situation rather than a recommendation.
Curcumin, the active compound in turmeric, is another target being investigated along anti-inflammatory lines. Since elevated inflammatory markers have been reported in people with OCD, and curcumin is one of the more potent natural anti-inflammatory compounds available, researchers have proposed it as a candidate for future trials. The hypothesis is reasonable, but OCD-specific clinical data is essentially nonexistent at this point. If you already take curcumin for joint pain or general inflammation, any OCD benefit would be an incidental bonus rather than something you can count on.