People don't need a prescription for it. It has virtually no side effects, which means it has no dropout rate, which in turn means people will keep coming back for more. In Germany, where St. John's Wort is prescribed and has been studied extensively, the herbal supplement is doled out four times more often than Zoloft. Finally, St. John's Wort has never been described as being effective for major depression. This is old news.
Most people take it for mild depression, for which studies have proven it works.