Many people turn to dietary supplements such as fish oil, vitamin D and herbal extracts in the hope of finding additional ways to ease depression. A large new analysis suggests that several compounds may have potential, but the researchers caution that much of the existing evidence is uncertain and vulnerable to bias.
Researchers conducted a network meta-analysis of 163 randomized controlled trials involving 15,757 adults with major depressive disorder. The studies evaluated 137 nutrient-based supplements and plant-derived compounds against placebo or standard antidepressant treatments.
Published in Molecular Psychiatry, the analysis examined changes in depressive symptoms, treatment response and dropout rates. Importantly, the researchers also investigated how study quality, risk of bias and unusually large results affected the overall findings. After less reliable evidence was accounted for, many initially promising effects became smaller or were no longer statistically convincing.
Only a few supplements stand out
Three interventions retained notable effects after stricter methodological checks. Eicosapentaenoic acid, or EPA, an omega-3 fatty acid found in fish oil, had the largest evidence base, with 20 trials involving 8,483 participants.
Vitamin D3 and a specific St John’s wort extract known as ZE117 were also associated with reductions in depressive symptoms compared with placebo. However, evidence for each came from only three trials, involving 344 participants for vitamin D3 and 207 for ZE117.
These relatively limited datasets reduce confidence in the apparent benefits, particularly for vitamin D3 and ZE117. Larger, well-designed and independently replicated trials would be needed to determine the size and clinical relevance of any effects.
Effects may be overstated
Study quality emerged as an important issue. Trials reporting unusually large benefits were more likely to have methodological limitations or a higher risk of bias.
Even after stricter criteria were applied, estimated effects for EPA, vitamin D3 and ZE117 remained larger than would generally be expected from robust antidepressant trials. This raised concerns that the apparent benefits may still be overestimated.
The findings do not demonstrate that these supplements are ineffective. Rather, they show that limitations in the available evidence make it difficult to determine their true effectiveness with confidence.
This distinction is particularly important because dietary supplements are often perceived as straightforward alternatives to conventional treatment. The current analysis does not provide evidence that they should replace established treatments for major depressive disorder.
Other plant-based compounds show signals
The analysis identified several other plant-derived compounds that could warrant further investigation. Some St John’s wort extracts were associated with favorable outcomes in individual analyses, although evidence varied according to the specific preparation and outcome examined.
Saffron was associated with a relatively large reduction in depressive symptoms, while curcumin showed potential effects on anxiety symptoms accompanying depression. However, these findings were supported by considerably smaller evidence bases than would be required for strong clinical conclusions.
Possible biological mechanisms have been proposed for these compounds. Saffron, for example, has been investigated for potential effects involving brain-derived neurotrophic factor, or BDNF, and neuroplasticity. Such mechanistic hypotheses, however, do not establish that the supplements effectively treat major depression in clinical practice.
Safety data remain incomplete
The analysis found no supplement category that was clearly less acceptable than placebo based on overall treatment discontinuation. Citicoline was an exception, with evidence suggesting higher dropout rates in some comparisons.
However, dropout rates provide only a limited measure of tolerability. Many trials lacked sufficiently detailed or long-term safety information, including data on rare adverse events and suicidality.
This is particularly relevant for products such as St John’s wort. Although it is available without prescription in some countries, it can interact with numerous medications, meaning that “natural” should not be interpreted as inherently risk-free.
Overall, EPA, vitamin D3 and certain St John’s wort preparations emerged as potentially promising interventions, but the certainty surrounding their effects remains limited. The analysis highlights the need for larger, rigorous trials capable of producing more realistic estimates of benefit and better safety data.
For now, the findings do not support replacing established treatments for major depressive disorder with dietary supplements. Instead, they show that a small number of compounds deserve further investigation while much of the broader supplement literature remains too uncertain to support firm clinical conclusions.