St. John’s Wort is a plant which has been shown in many well controlled clinical trials to be more effective than placebo in treating mild to moderate depression (not transient sadness). In fact the evidence supporting its effectiveness is better than the evidence supporting the effectiveness of some FDA approved anti-depressants.
It does not, in our experience, work as well for more severe forms of depression.
St. John’s Wort appears to be very well tolerated, with significantly fewer side effects than many antidepressants. In addition to (usually mild) GI distress, some people do experience anxiety, fatigue, headache and skin rash. Also, as with any antidepressant, it can trigger mania in someone with bipolar. And there are reports of hair loss and sexual side effects, as well as reports of a withdrawal syndrome similar to withdrawal from antidepressants (taper the supplement if you decide to stop taking it).
Exactly which ingredients are the effective ones remains a bit unclear. Many of the manufacturers standardize the dose to a certain content of hypericin. Some studies have suggested that hyperforin content may be more closely tied to effectiveness, and still others suggest that it is the mix of all of the seven or more potentially active ingredients that is critical.
As with any supplement, a regular dose of a therapeutic amount of St. John’s Wort can be expensive, and you need to take it regularly in order to see a benefit. For that reason you will want to ensure the quality of what you buy.
The only source of reliable quality information about herbal supplements is Consumer Labs. They just released a review of ten St. John’s Wort products (from manufacturers such as Walgreens, Nature’s Bounty, GNC, etcetera) and overall the results were good.
Still, it is well worth subscribing to Consumer Labs for a year (33$) and checking out the full report if you want to try taking St. John’s Wort.