Walk down any pharmacy aisle and you’ll find dozens of herbal products and supplements promising to lift your mood. But which ones actually work?
A massive new review analyzing 209 clinical trials offers the clearest picture yet of what science knows—and doesn’t know—about over-the-counter treatments for depression.
Researchers at Liverpool John Moores University and University College London sifted through nearly 24,000 studies to identify rigorous clinical trials testing 64 different products. Their findings, published in Frontiers in Pharmacology, reveal a landscape where a handful of supplements show solid evidence while dozens more remain largely untested.
The Heavy Hitters
Five products dominated the research landscape, each backed by substantial trial evidence. Omega-3 fatty acids led the pack with 39 studies, though results were mixed—more trials showed no benefit than positive effects when compared to placebo.
St. John’s Wort, tested in 38 trials, performed better. Most studies found it more effective than placebo for depression, and it matched prescription antidepressants in effectiveness. But here’s the catch: it can interfere with other medications, which is why UK health guidelines advise against it.
Saffron emerged as a surprising contender with 18 trials. The expensive spice showed positive effects in most studies and performed similarly to prescription drugs when tested head-to-head. Probiotics and vitamin D rounded out the top five, both showing promise in reducing depressive symptoms.
The Promising Underdogs
Several products showed encouraging results despite limited testing. The research team identified these as priorities for future study:
- Folic acid: Tested in 8 trials with mostly positive results
- Lavender: Six studies found benefits, whether consumed as tea, capsules, or tincture
- Zinc: Four trials showed promise for this essential mineral
- Tryptophan: The amino acid showed effects in 3 trials
- Lemon balm: Three studies found mood benefits from this common herb
What’s particularly intriguing is how these products align with traditional medicine. Many have been used for centuries to treat mood disorders, and modern research is beginning to validate some of those ancient practices.
The Science Behind the Claims
Why might these natural products work? The mechanisms vary widely. Some, like tryptophan, provide building blocks for mood-regulating brain chemicals like serotonin. Others, including lavender and chamomile, appear to reduce inflammation—a process increasingly linked to depression.
Zinc and folic acid help regulate brain-derived neurotrophic factor, a protein crucial for brain health. Probiotics may work through the gut-brain connection, influencing mood through the complex communication network between digestive bacteria and the brain.
The review found 89 trials tested supplements alongside prescription antidepressants, suggesting these products might work best as add-ons rather than replacements for conventional treatment. Remarkably, few safety concerns emerged from this combined approach.
The Reality Check
For all the promise, the research reveals significant gaps. Forty-one products have been tested in just one trial each—hardly enough to draw firm conclusions. Popular items like multivitamins and melatonin showed mixed results despite widespread use.
Sample sizes were often small, with a median of just 62 participants analyzed per study. That’s concerning because smaller antidepressant trials tend to overestimate benefits. Most studies also lasted only weeks, leaving questions about long-term effects unanswered.
Perhaps most telling: while researchers found evidence for 64 different products, surveys show people commonly use items like ginseng, ginkgo, and peppermint for depression—products with virtually no clinical testing.
What This Means for You
The research doesn’t provide a simple answer about which supplement to choose. Even products with strong evidence varied widely in dosage and preparation methods. St. John’s Wort studies, for instance, used different extracts and doses, making it difficult to know what works best.
Safety appeared good overall, with 85% of studies reporting no concerns. Only one trial—involving omega-3s—found increased serious adverse events, though the connection wasn’t clear. Still, the researchers noted that nearly one-third of studies failed to adequately report safety data.
Lead researcher Rachael Frost emphasized that anyone considering these products should consult healthcare providers, especially if taking other medications. The landscape of supplement-drug interactions remains poorly mapped, particularly for newer products.
The Path Forward
Rather than more studies of omega-3s or St. John’s Wort, researchers say future trials should focus on promising but under-tested products like lavender, lemon balm, and chamomile. These herbs are widely available, traditionally used for mood disorders, and show preliminary clinical promise.
The team also called for studies combining supplements with psychotherapy—not just medication. With talk therapy increasingly recommended as first-line depression treatment, understanding how natural products might enhance its effects could prove valuable.
For now, the message is nuanced: some over-the-counter options show genuine promise, but the evidence remains incomplete. In a field where hope often outpaces science, this comprehensive review offers both encouragement and a healthy dose of scientific skepticism.
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