Supplements for OCD: Evidence and Caveats

Obsessive-compulsive disorder (OCD) is typically treated with SSRIs and Cognitive Behavioural Therapy. Many patients are interested how they can make use of supplements as an adjunct to conventional treatment approaches. Research on supplements is still somewhat limited but growing.
See below summary for supplements that have some clinical evidence. For each supplement we note what the treatment mechanism is and what trials show. Always discuss supplements with your doctor as they can interact with medication and have side effects. This is not medical advice.

​N-Acetylcysteine (NAC)

NAC is an antioxidant that is derived from cysteine. It modulates glutamate neurotransmission. In OCD trials (typically over 12 weeks using 2.4–3.0 g/day), NAC has reduced symptom severity. A systematic review found NAC “reduces the severity of symptoms, with a good tolerability profile”. It may help with compulsions and is often studied as an add-on to SSRIs. Typical dosage is 2–3 g/day (split AM/PM).

• Mechanism: Increases brain glutathione (antioxidant) whilst regulating glutamate, which may calm overactive brain circuits that are linked to OCD.
  
• Evidence: Several small trials/case reports indicate a beneficial effect. For example, one trial showed significantly lower Yale–Brown OCD scores on NAC vs placebo. (However, studies are small and more research is needed.)
  
• Safety: Well-tolerated; common side effects include mild nausea, rash, constipation or gas. It has a sulfurous odor (odorless formulations exist). No major drug interactions noted, but always check with your doctor.
  
• Caveat: NAC is NOT to be seen as a replacement for standard OCD treatments. It’s an adjunct (often used with medication/therapy).
  

​Myo-Inositol

Myo-inositol (MI) is a nutrient that is in involved in cell signaling (including serotonin and glutamate pathways). In one placebo-controlled trial, 18 g/day of MI (monotherapy) improved OCD symptoms. However, adding MI to an SSRI offered no additional benefit over SSRI alone. This suggests MI might help some patients if used instead of (not with) medication. Research is limited.

• Mechanism: Influences inositol-related signaling in neurons. This could be affecting neurotransmitters involved in OCD.
• Evidence: One study with a small sample size found that MI alone reduced OCD severity. But the evidence is quite sparce.
• Safety: High doses (15–18 g) are required and side effects are mostly GI (bloating, gas, diarrhea). These usually lessen over time.
• Note: MI is generally safe but high-dose powders are bulky.

​Omega-3 Fatty Acids (EPA/DHA)

Omega-3s (fish oil) have many anti-inflammatory and neuroprotective effects. However, one small trial (11 OCD patients that were on a stable course of SSRIs) added 2 g/day EPA and found no significant improvement that was beyond placebo. The current state of evidence does not support omega-3s for OCD specifically. However, omega-3 supplements are generally safe and may infer benefits for mood and heart health.

• Mechanism: Omega-3 is thought to modulate neuronal membranes, inflammation and neurotransmission. The exact effect on OCD is unclear.
  
• Evidence: Only one published OCD trial (EPA vs placebo) which showed no benefit. Meta-analyses have found a beneficial impact of omega-3s with depression/anxiety. Trials focused in treating OCD are however lacking.
  
• Safety: Side effects are mild (heartburn and nausea). Beware that high doses can thin blood.
  
• Caveat: Omega-3s can be used for general health, but are not a replacement for OCD therapy.
  

​St. John’s Wort (Hypericum)

St. John’s Wort is an herbal antidepressant with mixed results for treating OCD. An early open-label study showed symptom improvement, but a subequent trial found no benefit over placebo. In general, SJW appears to be ineffective for treating OCD.

• Mechanism: May increase serotonin (among other neurotransmitters), but its effect on OCD circuits is unproven.
• Evidence: Only two small studies exist. The controlled trial failed to show an improvement. SJW may help with treating comorbid depression, but not OCD.
• Safety: Side effects can include insomnia, headache and GI upset but are usually mild. Important: SJW strongly interacts with many medications (SSRIs, birth control, anticoagulants) and it can make sense to avid taking it when taking other drugs.
• Caveat: Due to a lack of benefit and potential drug interactions, SJW is generally not recommended for treating OCD.

​Borage (Starflower) and Milk Thistle

These herbal remedies have one small trial each for managing OCD (from the same research group out of Iran).

• Borage: An Omega-6 source thought to affect serotonin transport. A 4–6 week trial reported reduced OCD and anxiety symptoms with borage extract. However, this is preliminary. Use only PA-free (pyrrolizidine alkaloid-free) borage products to avoid toxicity.
• Milk Thistle (Silybum marianum): Traditionally a liver tonic. One trial (6 weeks) found results that are comparable to fluoxetine in OCD. But this is a single study and unreplicated.
• Caveat: Because the available data is weak, borage and milk thistle remain unproven. Discuss liver enzymes and pay attention to quality if considering them.

Tryptophan and 5-HTP

These are natural serotonin precursors. No controlled studies show any benefit for treating OCD. High doses can cause fatigue, headache and nausea. Combining them with SSRIs can trigger serotonin syndrome (overload of serotonin). Due to lack of proof and safety concerns, tryptophan/5-HTP are not recommended supplements.

​Vitamins and Minerals

Some nutrients have been studied: OCD patients often have low vitamin D and occasionally low B12 or folate.

• Vitamin D: Studies find most OCD patients are vitamin-D deficient and low vitamin D correlates with worse OCD symptoms. No large trials have tested high-dose vitamin D in OCD, but correcting a deficiency is wise for overall brain health which may help boost mood. It is recommended to use standard doses and avoid exceeding safe upper limits.
  
• B Vitamins: Low B12 (and sometimes low folate) have been observed in OCD cohorts. While supplementing a deficiency is important, there’s no strong data that extra B12/folate meaningfully reduces OCD symptoms.
  
• Other Minerals: Magnesium and zinc can support general nervous system function. No specific OCD trials exist.
  

​Caution and Next Steps

Supplements can be a useful aid alongside standard OCD treatments, but they are not replacements for medication or cognitive-behavioural therapy. Always talk to a doctor before starting any supplement. Reliable brands are recommended in order to ensure quality.