What Safety Questions Should I Ask Before Taking St John's Wort?

Can I take St John's wort with sertraline or another SSRI?

No. The NHS states plainly: do not use St John's wort while taking sertraline. Sertraline is an SSRI, and the same interaction question matters for other antidepressants that affect serotonin.

This is not a minor “herbs versus medicines” technicality. According to the National Center for Complementary and Integrative Health, combining St John's wort with certain antidepressants can cause a potentially life-threatening increase in serotonin. Symptoms can begin within minutes to hours and include agitation, diarrhoea, a fast heartbeat, high blood pressure, hallucinations, and increased body temperature.

The decision rule is simple: do not run an unsupervised overlap. If concerning symptoms such as fast heartbeat, sweating, shaking, muscle twitching, confusion, or agitation occur while using sertraline, the NHS identifies these as possible signs of the rare but serious serotonin syndrome and says prompt medical advice is needed.

Switching is not the safe alternative if it is done abruptly. The NHS says people should not suddenly stop sertraline because withdrawal symptoms can occur; dose reductions are generally made gradually over weeks or months. A prescriber needs the full treatment picture before considering a change. The cost of skipping that conversation is not just uncertainty about mood symptoms; it is a preventable interaction or withdrawal problem.

Does St John's wort actually help anxiety or low mood?

For low mood and depression, the evidence is mixed; for anxiety, the available research does not establish that St John's wort helps, and it may worsen anxiety for some people.

The useful distinction is between a promising result and a dependable answer. The Cochrane review evaluated 29 randomised trials involving 5,489 people with depression, using extracts for 4 to 12 weeks. In nine larger placebo-controlled trials, the combined response-rate ratio for St John's wort compared with placebo was 1.28. Against SSRIs, the response-rate ratio was 1.00 across 12 trials.

Those figures do not mean every product or every person gets the same result. Cochrane cautions that its findings apply only to the preparations tested, or extracts with similar characteristics, and that products vary substantially. It also found more favourable results in German-speaking countries than elsewhere. That variation matters because the label “St John's wort” is not a guarantee that a product matches what was studied.

Specific trials add an important counterweight. NCCIH reports that a 2011 trial of 73 participants over 12 weeks found neither St John's wort nor citalopram outperformed placebo for minor depression. In a 2012 analysis of a 26-week trial involving 124 participants, St John's wort, sertraline, and placebo were similarly effective for moderate major depression.

For anxiety, do not borrow the depression evidence and call it proof. NCCIH says St John's wort may worsen feelings of anxiety in some people, while the evidence for its long-term effects is more limited than the short-term evidence. That makes “it is natural” the wrong screening question. The better question is: “What is the evidence for my symptom, and what could this product interfere with?”

How long does St John's wort take to work?

The available studies assessed St John's wort over 4 to 12 weeks, but the evidence does not support a universal timeline for when an individual will feel better.

That distinction keeps expectations realistic. Cochrane's reviewed trials used extracts for 4 to 12 weeks, while NCCIH describes a 12-week trial for minor depression and a 26-week trial for moderate major depression. Those are study durations, not a promise that a supplement will work by a given day or at all.

Use the time before starting to reduce the real risk: incomplete medication information. NHS Specialist Pharmacy Service advises people not to stop conventional medicines without consulting a healthcare professional and to include supplements on medication lists. A pharmacist conversation works best when it is a full inventory, not a partial reveal.

A strong opening line for that conversation is: “I am considering St John's wort for low mood or anxiety. Can you check it against every medicine and contraceptive I use, and tell me what symptoms would need prompt medical advice?” Clear input creates a safer answer.