St. John’s Wort (Hypericum perforatum extract) is a weak inhibitor of monoamine oxidase (MAO), which destroys monoamine neurotransmitters including dopamine in the brain and leads to low spirits. St. John’s Wort has also been shown to inhibit re-uptake of several neurotransmitters, such as serotonin, dopamine, noradrenaline, and GABA in the brain, and to reduce expression of interleukin-6.43 Each of these actions can contribute to alleviating low mood status by slowing the recycling of neurotransmitters needed for maintaining emotional balance. Flavonoids, hypericin and pseudo-hypericin, are the constituents thought to be associated with the benefits of St. John’s Wort. In particular, hypericin appears to be the active ingredient.44-49

Side effects can include insomnia, vivid dreams, restlessness, anxiety, agitation, irritability, gastrointestinal discomfort, fatigue, dry mouth, dizziness, and headache. Do not use if taking digoxin unless under a doctor's care. When using St. John's Wort, avoid prolonged sunlight exposure. Concomitant use with oral contraceptives may decrease steroid concentrations, resulting in breakthrough bleeding and irregular menstrual bleeding. Effectiveness of antiretroviral drugs may be reduced.