St. John's wort (Hypericum perforatum) is a European herbal remedy widely used to treat depression. Many people find that it improves their outlook and sense of equilibrium without creating the feeling of being drugged. A number of trials of St. John's wort as a treatment for mild to moderate depression have been done, and clinical improvements have been observed. Although test-tube studies found that hypericin, one active ingredient in St. John's wort, has antiretroviral properties when exposed to light, it is not useful for the management of HIV infection.

St. John's wort is usually sold as a standardized extract (0.03% hypericin or 3% hyperforin), although it can also be taken as an oil, a tincture or a tea. Its most frequently reported side effect is photosensitivity, which means that it will make you more sensitive to the sun and increase your risk of sunburn and rash. St. John's wort interacts with many medications, including antidepressants, birth control pills, Viagara, transplant drugs, amphetamines, narcotics, methadone and some over-the-counter cold and flu remedies. St. John's wort may also interact with street drugs and methadone.

St. John's wort (including its extracts) interacts with antiretroviral drugs (protease inhibitors and non-nucleoside reverse transcriptase inhibitors). This interaction can significantly impact your health by increasing side effects. It also can weaken the effectiveness of HIV medications, leading to treatment failure, drug resistance, and reduced options for future treatment. If you want to use St. John's wort or any of its extracts, it is very important that you discuss this with all of your health care providers, including your doctor, pharmacist and natural health practitioner (see the section in this guide called Herb-Drug Interactions).

St. John's wort should not be used by people with high blood pressure.