Understanding the research landscape of over-the-counter herbal products, dietary supplements and medications evaluated for depressive symptoms in adults: A scoping review

Rachael Frost^1*Aiman Zamri¹Silvy Mathew¹Adriana Salame¹Cini Bhanu¹Sukvinder Kaur Bhamra²Juan Carlos Bazo-Alvarez^1,3Michael Heinrich¹Kate Walters¹

• ¹University College London, London, United Kingdom
• ²Medway School of Pharmacy, Faculty of Sciences, University of Kent, Chatham, United Kingdom
• ³Faculty of Medicine, Cesar Vallejo University, Trujillo, Peru

Background: Over-the-counter (OTC) products such as herbal medical products or dietary supplements are a valued part of preventative and supportive self-care for depressive symptoms, but there is a wide array of products available with differing levels of clinical evidence. It is unclear what the optimal directions for future research are in this field.Aims: We aimed to scope the size and nature of the evidence base available for OTC products for depression in adults aged 18-60.Methods: We carried out a scoping review following Joanna Briggs Institute guidance. We searched MEDLINE, EMBASE, PsycInfo, AMED and CENTRAL from inception to December 2022, and 10% results were screened by two authors and the remainder by one author. We included randomised controlled trials of products commonly available OTC in multiple countries in participants with symptoms or a diagnosis of depression. Results were narratively summarised by product and volume of evidence available.Results: Out of 23,933 records found, we screened 1367 full texts and included 209 trials. The largest volume of evidence was for omega-3s, St John's Wort, saffron, probiotics and vitamin D. Out of a range of products with promising evidence, those most commonly used and so warranting further research were lavender, lemon balm, chamomile and echium. For 48 products we found only single trials. Few products presented safety issues, whether used alone or adjunctly to antidepressants.Conclusions: Products with limited but promising evidence included folic acid, lavender, zinc, tryptophan, rhodiola and lemon balm, and future research should focus on these products. There is a need for further evaluation of herbal medical products as adjuncts to antidepressants, as well as a need to explore the benefits of products adjunctively to psychological therapies for a more integrative approach. Safety reporting needs to be further improved in these trials.