An Adelaide study has shown St John’s Wort can produce the same adverse reactions as antidepressants – including dangerous increases in body temperature and blood pressure.

The study has also uncovered the possibility of serious side effects when St John’s Wort is taken along with prescription antidepressants.

The University of Adelaide research, published this month in the journal Clinical and Experimental Pharmacology and Physiology, has prompted a pharmacologist to call for better warnings on packaging of St John’s Wort.

The study compared reported adverse drug reactions from the popular herbal remedy with fluoxetine – a commonly prescribed antidepressant.

It found the adverse reactions were identical.

University of Adelaide pharmacology PhD student Claire Hoban said that St John’s Wort, “like all herbal medicines”, was a drug.

“Importantly, it is a drug that can cause serious side effects such as dangerous increases in body temperature and blood pressure,” she said.

“There is a common belief that because something is natural and can be purchased from a health food shop without a prescription, it’s safe.

“However, people need to start thinking of St John’s Wort, and other herbal medicines, as a drug and seek advice from a qualified healthcare practitioner to be sure they use it safely.

“It’s concerning to see such severe adverse reactions in our population, when people believe they are doing something proactive for their health with little risk.”

Hoban told InDaily that use of St John’s Wort along with a prescription medications had the potential to cause severe medical problems, even death.

For example, the natural remedy is a blood thinner, so use in conjunction with the commonly prescribed anticoagulant Warfarin could lead to a haemorrhage.

Like common antidressants, the active ingredient in St John’s Wort is a selective serotonin re-uptake inhibitor (SSRI). Hoban said that taking both St John’s Wort and a prescription SSRI could lead to serotonin syndrome, a potentially fatal condition where the body’s system is flooded with serotonin, causing damage to the nervous system.

The study examined reported adverse reactions over the years from 2000 to 2013: 84 to St John’s Wort and 447 to fluoxetine.

“While there were fewer confirmed cases of side effects for St John’s Wort, we know that less people use St John’s Wort and adverse reactions for herbal medicines largely go unreported because they are not considered drugs,” Hoban said.

“Furthermore, we found that the reported reactions for St John’s Wort were very similar to fluoxetine, which included anxiety, panic attacks, dizziness, vomiting, amnesia and aggression.”

Hoban said the evidence was mixed about the efficacy of St John’s Wort in treating depression.

University of Adelaide pharmacologist and toxicologist Dr Ian Musgrave said “the real danger” was that people could access St John’s Wort without a prescription, meaning there was no control over dosage or its use in conjunction with other drugs.

“Most people taking St John’s Wort will not have any adverse reactions; however, those who do take it should tell their doctor and pharmacist,” he said.

“It’s important that doctors and pharmacists know about all the drugs their patients take, not just prescription drugs, because herbal medicines like St John’s Wort can have serious reactions with some pharmacy medicines, like antidepressants, the contraceptive pill and some blood thinners.

“Based on this research, I’d also like to see bottles of St John’s Wort containing improved warnings of the potential adverse reactions.”

Hoban said the extent and quality of current warnings depended on the brand of St John’s Wort.

She said pharmacies should be warning patients of the potential side-effects and interactions with other drugs when people purchase St John’s Wort.

“I believe this is a really important message that needs to get out there,” she said.

– InDaily