"I liked your column last week and want to try plant medicine. I'm stressed and have low moods. Can I take St. John’s Wort? I take the pill and have heard some conflicting information."

The safety of St. John's Wort is a very topical question as it is one of the most used medicinal plants worldwide. In European countries it is available as a prescription medicine and outsells pharmaceutical anti-depressants.

Numerous studies have shown that it is equivalent in effectiveness to synthetic selective serontoin reuptake inhibitors (SSRIs) in mild to moderate depression but has a better safety profile and is very well tolerated. Nevertheless, this herb has had a lot of attention due to its alleged ability to interact with pharmaceutical medication.

One of the most common concerns that people have is if it is OK to take St. John's Wort alongside other medication, such as the oral contraceptive pill. Considering that millions of people worldwide take St. John's Wort, many of them women on the Pill, reports of actual herb-drug interactions and side effects are very rare.

Many of the initial and even current concerns raised were based on theoretical considerations, test tube experiments or studies that used chemically purified single constituents of St. John's Wort instead of testing the whole plant in real people.

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Interestingly, the herb-drug interaction issue only became prominent in the late 1990's, when some German manufacturers artificially stabilised and concentrated the hyperforin content of their St. John's Wort tablets, as they believed that this active constituent was responsible for the anti-depressant action. All other remedies did not any show herb-drug interactions.

High levels of hyperforin can induce cytochrome P450 (CYP) enzymes, a detoxification system which the journal Science nicknamed the 'garbage disposal' system of the liver and small intestine.

The job of these enzymes is to protect the body against toxins and xenobiotics - that's a good thing! However, they also clear out certain synthetic drugs with a therapeutic narrow window faster than intended, which leads to lower blood concentrations of the drug and compromises its efficacy.

Hyperforin is a constituent which degrades quickly, and the amount needed to induce the P450 enzyme pathways are not found in traditional preparations such as medicinal teas or ethanol extracts used in oral liquids. There is also no interaction between a topical formulation, for example a herbal cream or oil containing St. John's Wort and a pharmaceutical drug.

It is the type of preparation (standardised tablet versus traditional tea or liquid), the dosage, and the concentration of hyperforin that will determine if the St. John's Wort remedy has herb-drug interaction potential or not. Scientific studies confirmed that there are not safety concerns in remedies with less than 3.5mg of hyperforin, which means that they can be safely taken in conjunction with pharmaceutical drugs.

Because reliable contraception is crucial for the peace of mind of many women, further scientific studies were undertaken to test contraceptive cover in women who took concurrently the Pill and St. John's Wort.

They established that St John's Wort does not change hormonal levels or reduce the effectiveness of the Pill, meaning that all women in the trials maintained full protection when taking a low-dose pill and St John's Wort together. However, there was a higher rate of breakthrough bleeding in the St. John's Wort groups. Women should always take their pill, even if breakthrough bleeding occurs. There is no evidence of a mass outbreak of unwanted pregnancies in women taking St John's Wort.

In March of 2014, Medsafe New Zealand confirmed that St John's Wort, which is low in hyperforin is unlikely to produce interactions. The Swiss government made the same declaration in 2002.

Unfortunately, Medsafe also stated that "...most products contain 3 per cent [this should have said 3mg] hyperforin", however this is not the case in the New Zealand market.

Registered medical herbalists are well versed in the safe use of St. John's Wort and can be contacted via the official website of the New Zealand Association of Medical Herbalists.

St John's Wort is one of the most widely used and researched herbs in the world. As a traditional preparation, it has an excellent safety and efficacy record. You can feel confident using this stress relieving, energising and uplifting herb, even when you are on the Pill.

Each week Sandra will answer reader questions about health issues and discuss how plant medicine may be able to help you.

Always seek advice from your GP or call 111 in health emergencies.