St. John’s Wort

St. John’s wort is natural. It’s an herbal supplement that doesn’t require a prescription and you can buy it at a health food store.

Sounds good, but that doesn’t necessarily make it harmless, according to a new study published in the journal Clinical and Experimental Pharmacology and Physiology.

Researchers at the University of Adelaide compared adverse events of St. John’s wort and the antidepressant drug fluoxetine (Prozac). The team used information from doctors’ reports to Australia’s national agency on drug safety.

St. John's Wort

Between 2000 and 2013, there were 84 adverse reaction reports for St. John’s wort. There were 447 reports for Prozac. Since reporting adverse events is voluntary, researchers said it’s likely that adverse events are underreported.

Side effects of the two substances are similar. They include vomiting, dizziness, anxiety, panic attacks, aggression, and amnesia. There are also serious concerns about drug interactions.

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The Benefits of St. John’s Wort

St. John’s wort (Hypericum perforatum) is a flowering plant.

The flowers are used to make liquid extracts, pills, and teas. The popular herbal therapy is often used to ease symptoms of depression. People have been using St. John’s wort for centuries.

A Cochrane systematic review found that St. John’s wort can be effective in treating major depression. However, the Food and Drug Administration (FDA) has not approved it for that purpose.

Licensed naturopathic physician Jeremy Wolf explained that St. John’s wort creates many actions in the body.

“[St. John’s wort] is a strong antidepressant and may elevate mood in individuals with mild to moderate depression.
Jeremy Wolf, licensed naturopathic physician

“It is a strong antidepressant and may elevate mood in individuals with mild to moderate depression,” he said.

He notes that St. John’s wort is not recommended for individuals with severe depression.

Wolf said St. John’s wort also has strong antiviral activity that may also promote healing and repair of wounds.

He cautioned that the herb is not a fast-acting cure. It may take weeks or months before you notice any effect.

How much St. John’s wort should you take?

Blair Green Thielemier, PharmD, told Healthline that dosing varies due to non-standardized manufacturing.

A normal dose range would be anywhere from 300 to 1200 mg a day. It’s usually taken in divided doses (300 mg three times daily or 600 mg twice daily).

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The Downside of St. John’s Wort


FDA regulations for dietary supplements are not the same as those for drug products. Unless there's a new dietary ingredient, a firm doesn't have to provide FDA with the evidence it relies on to substantiate safety or effectiveness before or after it markets its products.

“Natural" doesn’t mean it can’t cause harm, said Thielemier.

The main concerns about the herb center on the metabolic pathway known as cytochrome 450. She explained that this pathway consists of the enzymes our body uses to clear drugs and ingested chemicals from the bloodstream.

“These enzymes are responsible for breaking down everything from the glass of wine you may have with dinner to a daily vitamin you take to keep your bones strong,” said Thielemier.

Other substances can influence these enzymes.

“If you have ever heard that grapefruit juice can interfere with your medications, then you know of this process we call enzyme induction,” said Thielemier. “St. John's wort, like grapefruit juice, induces the body to produce more of these enzymes in order to clear the chemical from the bloodstream [faster].”

That can rob other medications of their power.

Wolf suggests the herb may work similarly to fluoxetine. If it inhibits the reuptake of serotonin, it would explain the similar side effects.

It also interacts with many common pharmaceuticals.

The problem lies in the insane costs of proving safety and efficacy through clinical trials.
Blair Green Thielemier, PharmD

“When combined with SSRIs [selective serotonin reuptake inhibitors] and MAO [monoamine oxidase] inhibitors, it may lead to elevated blood pressure and could induce what is known as serotonin syndrome,” said Wolf. “This includes confusion, fever, agitation, rapid heart rate, shivering, perspiration, diarrhea, and muscle spasms.”

According to the National Center for Complementary and Integrative Health, in addition to antidepressants, St. John’s wort interacts with oral contraceptives, anti-seizure medications, and anticoagulants. It can also interfere with anti-rejection medications, heart medications, and some drugs used for heart disease, HIV, and cancer.

Wolf noted that pregnant or breastfeeding women should avoid St. John’s wort. So should people who are sensitive to sunlight, as the herb can intensify the effect.

Regulation Process Not the Same as Drugs

Should natural and herbal products include warnings and go through the same rigorous testing as prescription drugs?

Thielemier thinks so.

“How else will we know whether they are safe and effective? The problem lies in the insane costs of proving safety and efficacy through clinical trials,” she said. 

“I always advise individuals and remind them of the importance in checking with their healthcare provider or a trained practitioner before starting supplements and herbs due to the potential for side effects and interactions,” said Wolf.

Read More: Should the FDA Regulate Vitamins, Herbs, and Other Supplements? »