Mood Supplements and Their Evidence: St. John's Wort, Vitamin D, and Omega-3

Many adults reach for supplements to support their mood, but the evidence behind each one varies considerably. This guide summarises what the NIH Office of Dietary Supplements (ODS) and related agencies report about three of the most commonly discussed options, so you can have a more informed conversation with your clinician.

Please note: supplements are not intended to diagnose, treat, cure, or prevent any disease, and these statements have not been evaluated by the FDA.

St. John's Wort

What it is and how it may work

St. John's Wort is a plant-based supplement, not an essential nutrient, and it has no established role in normal human physiology. It has been used traditionally for low mood and wound healing. Laboratory research suggests its constituents may affect chemical messengers such as serotonin in the brain, though the exact mechanism in people is not fully established, according to the NIH National Center for Complementary and Integrative Health (NCCIH).

What the evidence shows

• Mild to moderate depression (Moderate evidence): Research suggests St. John's Wort may be more effective than placebo and roughly as effective as standard antidepressants for mild to moderate depression. This is the strongest evidence available for any mood-related use.
• Severe depression or use beyond 12 weeks (Insufficient evidence): There is not enough reliable evidence to support its use for severe depression or for periods longer than approximately 12 weeks.
• Menopausal symptoms and hot flashes (Limited evidence): Some research hints at a possible benefit, but evidence remains limited.
• Other uses including ADHD, OCD, IBS, PMS, and smoking cessation (Insufficient evidence): Current evidence does not support these uses.

Safety and interactions

For most adults who are not taking any medicines, St. John's Wort appears to be safe when taken by mouth for up to 12 weeks. The safety of longer use has not been established. It may be unsafe during pregnancy.

St. John's Wort interacts with a very large number of medicines. Key interactions reported by the NCCIH include:

• Antidepressants (SSRIs, SNRIs, tricyclics such as amitriptyline, and bupropion): Combined use can raise serotonin to dangerous levels and cause serotonin syndrome.
• Oral contraceptives: St. John's Wort can reduce their effectiveness, leading to breakthrough bleeding and unintended pregnancy.
• Cyclosporine and transplant anti-rejection drugs: Drug levels can drop, risking organ rejection.
• Warfarin and other anticoagulants: The blood-thinning effect may be reduced.

Always talk to a doctor or pharmacist before combining St. John's Wort with any prescription medication.

Vitamin D

What it is and how it works

Vitamin D is a fat-soluble nutrient with well-established roles in the body. According to the NIH ODS, it promotes calcium absorption in the gut, maintains adequate serum calcium and phosphate concentrations for normal bone mineralisation, and supports bone growth and remodelling. It also helps prevent hypocalcemic tetany, which involves involuntary muscle contractions and cramps.

Reference values (NIH ODS)

The adult target intake is 15 mcg (600 IU) per day, rising to 20 mcg (800 IU) for adults aged 71 and older. The Tolerable Upper Intake Level from all sources combined is 100 mcg (4,000 IU) per day for everyone aged 9 and older, including during pregnancy and lactation. Exceeding the upper limit raises the risk of hypercalcemia. A clinician may prescribe higher doses in specific medical situations, but this should only happen under supervision.

What the evidence shows for mood and beyond

• Bone health (Strong evidence): Vitamin D promotes intestinal calcium absorption and maintains the mineral concentrations needed for normal bone mineralisation. Deficiency causes rickets in children and osteomalacia in adults.
• Bone density in older adults (Moderate evidence): Vitamin D combined with calcium supplements can modestly increase bone mineral density in some postmenopausal women and older men, and may reduce fracture rates in institutionalised older people.
• Falls and fractures in community-dwelling older adults (Limited evidence): Some benefit has been observed but evidence is limited.
• Depression, cardiovascular disease, cancer, type 2 diabetes, or weight loss (Insufficient evidence): Despite widespread interest, the NIH ODS rates evidence for all of these outcomes as insufficient. Vitamin D supplements have not been shown to prevent or treat depression.

Interactions to know

• Orlistat: Can reduce absorption of vitamin D from food and supplements.
• Statins: High-dose vitamin D supplements may reduce how well statins work.
• Corticosteroids such as prednisone: Can lower blood levels of vitamin D.
• Thiazide diuretics: Combined with vitamin D supplements, these can raise blood calcium to unsafe levels.

Omega-3 Fatty Acids (EPA and DHA)

What they are and how they work

Omega-3 fatty acids are a family of polyunsaturated fats. The NIH ODS explains that EPA and DHA serve as structural components of the phospholipids that form cell membranes, with DHA especially concentrated in the retina, brain, and sperm. They also act as precursors to eicosanoids, signalling molecules involved in cardiovascular, pulmonary, immune, and endocrine function, and they provide a source of energy.

Reference values (NIH ODS)

The Institute of Medicine set an Adequate Intake (AI) for ALA (the essential plant-derived omega-3) of 1.6 g per day for men and 1.1 g per day for women aged 19 to 50. No Recommended Dietary Allowance exists for ALA, and no specific intake targets have been set for EPA or DHA. No Tolerable Upper Intake Level has been established for any omega-3. The FDA specifies that supplement labels should not recommend more than 2 g of EPA and DHA combined per day.

What the evidence shows

• Cell membrane structure and ALA as an essential fatty acid (Strong evidence): These roles are well established.
• Lowering elevated triglycerides (Moderate evidence): EPA and DHA supplements have been shown to reduce elevated serum triglyceride levels.
• Rheumatoid arthritis symptom relief (Limited evidence): Some benefit has been observed but evidence is limited.
• Cardiovascular event prevention in the general population (Limited evidence): Evidence is limited and results across trials are mixed.
• Cognitive decline, dementia, depression, infant neurodevelopment, and macular degeneration (Insufficient evidence): The NIH ODS rates evidence for all of these outcomes as insufficient at this time.

Interactions and safety notes

Omega-3 supplements are generally regarded as safe. Side effects are usually mild and may include an unpleasant taste, heartburn, nausea, or loose stools. Because omega-3s can reduce platelet aggregation, combining them with anticoagulant or antiplatelet medicines such as warfarin, aspirin, or clopidogrel may theoretically increase bleeding risk. Clinical trials have generally not shown clinically significant bleeding, but periodic monitoring is advisable. High doses may also suppress immune responses. Prescription-strength omega-3 products used to lower triglycerides should only be taken under medical supervision.

Key Takeaways

• Of the three supplements covered here, St. John's Wort has the strongest mood-specific evidence, rated moderate for mild to moderate depression, but it carries serious drug interaction risks.
• Vitamin D has strong evidence for bone health but insufficient evidence for mood or depression specifically.
• Omega-3s have strong evidence for their structural roles in the body but insufficient evidence for mood or cognitive outcomes.
• All reference values in this guide come from the NIH Office of Dietary Supplements and the NCCIH.
• Consult a clinician or pharmacist before starting any supplement, particularly if you take prescription medications or have an existing health condition.