A literature study covering the use of St Johns Wort extract in the treatment of depression. It is a commonly used herb against depression, especially in Germany where it’s one of the most commonly prescribed drugs against depression. In Norway, it’s sold over the counter only at pharmacies and is a registered herbal medicinal drug.The active components of St Johns Wort extracts are many, one of them, hyperforin, is believed to be the most important constituent acting as an antidepressant. Many studies have been conducted on the antidepressant effects of St Johns Wort and all of the RCT’s included in this study have more or less come to the same conclusions.St Johns Wort extracts are as effective as commonly used chemical antidepressants, and have fewer side effects. It is also an herb widely known for its potential to interact with other commonly prescribed medicines. This is believed to be a result of the potent effect of St Johns Wort extracts as inductors of the Cytochrome P 450 system in the liver. Especially inducting CYP 3A4, an enzyme in the Cytochrome P450 system, a system responsible for metabolising over 50% of all drugs. A consequence of this being decreased plasma levels of coadministrated drugs resulting in less predictable therapeutic effect.