St. John's wort is a supplement derived from the Hypericum perforatum plant. It is used to treat skin wounds and can be an effective remedy for symptoms of depression. Despite its natural origin, St. John's wort can cause unwanted side effects. When combined with other herbs or medications, St. John's wort may cause dangerous interactions. Understanding the possible side effects of St. John's wort can help prevent unnecessary health risks.
Sun Sensitivity
Sun sensitivity is a common side effect of St. John's wort. Sun sensitivity can lead to an increased risk for sunburn, which is a major risk factor for many types of skin cancer. It is more likely to occur with high doses of St. John's wort and when taking oral contraceptives or antibiotics like doxycycline. Other skin reactions that may occur include rash, hives, itching and irritation.
To reduce the risks of sunburn when taking St. John's wort, wear protective clothing like sunglasses, long-sleeved shirts and large-brimmed hats when outdoors and avoid direct sun exposure as much as possible. People with light skin should apply sunblock before engaging in outdoor activities while taking St. John's wort, according to Rx List.
Nausea
Nausea is a possible side effect of St. John's wort. It may be more severe with higher doses or when taken on an overly full or empty stomach. Other gastrointestinal effects that may occur include constipation, cramping and abdominal discomfort.
Dry Mouth
Like tricyclic antidepressants, St. John's wort can cause dryness of the mouth and mucous membranes. It may be necessary to drink more water than usual to prevent dry mouth while taking St. John's wort. Avoiding caffeine, alcohol and other dehydrating substances can also help.
Drowsiness
Feelings of drowsiness and lethargy are relatively common when taking St. John's wort. The herb's effects on serotonin, norepinephrine and other neurotransmitters is a likely cause of fatigue. Drowsiness is a common side effect of many pharmaceutical antidepressants as well, including selective serotonin reuptake inhibitors (SSRIs), tricyclic antidepressants and mood stabilizers.
Taking St. John's wort close to bedtime may prevent daytime drowsiness while helping improve sleep quality. Do not attempt to drive or perform other dangerous activities until you know how St. John's wort affects you.
Drug Interactions
St. John's wort can change the way other herbs and medications affect the body. According to the American Cancer Society, St. John's wort may cause dangerous interactions with blood thinners, HIV medications and antidepressants like selective serotonin reuptake inhibitors and monoamine oxidase inhibitors (MAOIs). Taking St. John's wort with other medications may result in either a decrease or increase in the effects of such medications because of St. John's wort's effect on a liver enzyme system known as cytochrome P450.
To avoid dangerous interactions, ask your doctor before taking St. John's wort, especially if you take other supplements or medications on a regular basis.
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