St John's wort: benefits, dosage and side effects

You can buy St John's wort in supplements over the counter (without a prescription) at pharmacies and in health and wellness stores. Some people find it helpful, but evidence around St John's wort is still emerging and it can interact dangerously with certain medications and medical conditions – so it's important to check with your healthcare professional before using it.²

These yellow flowers can be known for their potential role in supporting mood. Research in adults with depression has compared St John’s wort with some commonly used anti-depressants, with some studies reporting similar outcomes.² A meta-analysis of studies covering over 3,000 participants, and ranging from the years 1966 to 2015, found that St John's wort performed similarly to selective serotonin reuptake inhibitor (SSRI) medications in response, remission and reduction of depression.³

However, the research has used specific St John’s wort extracts and doses, which can differ from those found in individual products. Evidence also varies depending on the population studied, with research into areas such as anxiety limited. It’s important to check with a doctor or healthcare professional before taking St John’s wort to make sure it’s suitable for you.

Evidence is less robust here, but two small studies looked at St John’s wort and hot flushes in women before, during and after menopause. After eight weeks, the studies found differences in how often hot flushes happened, how long they lasted and how strong they felt. St John’s wort has also been studied in relation to PMS, but the results were different depending on the symptoms studied, so more research is needed to understand these findings.^4,5

Research has looked at how St John’s wort may affect memory, thinking and how we process emotions. So far, the results are mixed. Some studies found differences in short-term memory or how people responded to positive and negative information, while others found no clear effect on memory or thinking.^6,7,8 St John’s wort contains a natural substance called hyperforin, which may affect brain chemicals linked to mood (such as serotonin and dopamine) and help them stay active for longer. However, more research is needed to understand these effects.

There's no set recommended dosage for St John's wort and it's not clear what quantity works best.¹⁰ Plus, quantities can vary significantly between individual supplements, so you should read the packaging and dosage information thoroughly and check with your healthcare professional before trying any products.

It's also possible to be allergic to St John's wort.¹¹

It's also recommended to limit alcohol.¹³ This isn't an exhaustive list however, so you should always check with a doctor before trying St John's wort to make sure it's safe for you.