Question: How long do I need to take a particular herb, vitamin or supplement to determine if it is effective?
Answer: Because many of these dietary supplements, such as herbs, are from a natural source, they're not typically concentrated or made to be very potent. In other words, they're not an extract and they're not a drug, so they tend to be milder in their onset. They take a little longer to see the effect. So for example somebody using St. John's wort for depression might need four to six weeks to see the benefit, whereas an anti-depressant drug might work even sooner than that.