St John’s wort

Also known as Hypericum or Hypericum perforatum

Key points about St John’s wort

  • St John’s wort is a herb that is sold as a natural health product in New Zealand at health food stores and pharmacies.
  • It is used for the treatment of depression and other conditions such as anxiety.
  • St John’s wort also known as Hypericum or Hypericum perforatum.
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St John’s wort (also called Hypericum or Hypericum perforatum) is a herb. Its flowers and leaves are used to make a plant product marketed for the treatment of depression and other conditions such as anxiety, symptoms of menopause and pain. 

  • In New Zealand St John’s wort is not registered as a medicine but is considered a herbal supplement or complementary medicine.
  • Although St John’s wort is a herb, it is still an active treatment that has specific chemical effects.
  • The mechanism of action of St John’s wort is not fully understood but it is believed to affect certain chemicals in your body, such as serotonin and noradrenaline. In this way it is thought to improve mood. 
  • St John's wort interacts with medicines used to treat depression and other illnesses. It is important to let your doctor or pharmacist know if you want to try St. John's wort so that he or she can check if it might interfere with other medicines you are taking.
  • There are no standardised St John's wort preparations in New Zealand. St John's wort is available in a variety of formulations such as tablets, capsules, liquid tinctures and teas from health food stores and pharmacies.  

Research has found that St John's wort is useful in the treatment of mild to moderate depression, but not effective in severe depression.

In an analysis of studies comparing St John’s wort with a placebo (sugar pills) and standard antidepressants (SSRIs or tricyclics), the authors found that compared with placebo, people taking St John’s wort were more likely to have an improvement in their symptoms. There were no significant differences in depression response rates between St John’s wort and standard antidepressants. The studies also found that patients taking St John’s wort were less likely to drop out of trials due to adverse effects than those taking standard antidepressants.

There are a number of products available on the market containing St John's wort (Hypericum). When buying St John's wort you should be careful about the potency (strength) and purity of the product. A standardised extract of 0.3% Hypericum is mostly used in clinical trials.

St John's wort is possibly effective for menopausal symptoms, plaque psoriasis, wound healing and somatisation disorder. Read more about St John's wort(external link) National Institute of Health.  

St John’s wort can be taken as tablets and capsules. You can also get it as a tea, and as a liquid called a tincture, which you can take as drops in water. There are additional products available that combine St John's wort with other herbs, such as lemon balm (Melissa officianalis) and hops (Humulus lupulus).

  • Because St John's wort is classified as a supplement, the strength and dose will vary depending on what brand of St John's wort you take. Always check the dosing instructions on the product label or packaging.
  • The effect of St John's wort is not immediate. You may need to take it for two to three weeks before you notice any improvement. If there is no change in your symptoms by then, it’s likely St John's wort will not be of benefit for you and you should talk to your doctor about other ways of managing your symptoms.

You should not use St John's wort if you:

  • are pregnant or planning a pregnancy
  • are breastfeeding
  • have bipolar disease
  • are taking antidepressants such as SSRIs, such as paroxetine, citalopram, fluoxetine, sertraline or venlafaxine
  • are taking triptan medication for migraine, such as sumatriptan, rizatriptan and zolmitriptan.

St John's wort interacts with a large number of medicines. In some cases, St. John's wort makes the medicines less effective and in other cases, it may make the effects of a medicine stronger, which can lead to more side effects.

Examples of medicines that interact with St John’s wort
  • Hormonal contraceptives such as the pill and implants
  • Warfarin and dabigatran
  • Calcium-channel blockers such as amlodipine, nifedipine and verapamil with concurrent use.
  • All anticonvulsants including carbamazepine, phenobarbital and phenytoin
  • Simvastatin and atorvastatin
  • Methadone
  • HIV treatments including indinavir, nelfinavir, ritonavir, saquinavir, efavirenz and nevirapine
  • Digoxin
  • Anti-cancer medicines

Note: the above list is not complete. Check with your doctor or pharmacist before starting St John’s wort or before starting any new medicines.

Although St John’s wort is a herb, it is still an active treatment that has specific effects and it can cause side effects. Side effects from St John's wort may include:

  • tummy upset
  • skin rash, hives or other skin rashes
  • feeling tired
  • restlessness
  • headache
  • dry mouth
  • feelings of dizziness or mental confusion.

Your skin can become more sensitive to sunlight. If you have light skin and are taking St John's wort, wear long sleeves and a hat when in the sun, and use a sunscreen with at least SPF15 or higher.

Risk of serotonin syndrome

Serotonin syndrome occurs when the level of serotonin in your brain gets too high. It can happen with the use of St John’s wort and some medicines such as SSRIs or the pain relief medication, tramadol.

  • You are at risk of serotonin syndrome if you just started taking or increased the dose of your St John’s wort or if you are taking St John's wort with other medicines that also increase serotonin levels.
  • Symptoms can range from mild, such as shivering and diarrhoea (runny poos), to severe, such as muscle rigidity, fever and seizures.
  • Milder forms of serotonin syndrome may go away within a few days of stopping the medicines that caused your symptoms.
  • Severe serotonin syndrome needs hospital admission and can be fatal if not treated.
  • Read more about serotonin syndrome.

Withdrawal symptoms

Some people may get withdrawal symptoms when they stop taking St John’s wort abruptly, such as feeling sick, dizzy and feeling tense. As St John’s wort has similar properties to prescribed antidepressants, it is advisable to slowly reduce your dosage so as to lessen the chance of withdrawal symptoms, especially if you have been taking it for longer than a few weeks.

Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)

The following links provide further information on St John's wort. Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Can I take St John's Wort with other medicines?(external link) Medsafe, NZ
St John's wort as a depression treatment(external link) BlackDog Institute, Australia 
Making sense of St John's wort(external link)
St John's wort(external link) Patient Info, UK
St. John's wort(external link) NHS Foundation Trust 
St John's wort (external link) National Center for Complementary & Integrative Health Clearinghouse, US


5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


  1. Linde K, Berner MM, Kriston L. St John's wort for major depression(external link)Cochrane Database Syst Rev. 2008 
  2. Linde K, Berner MM, Kriston L. St John's wort for depression.(external link)Cochrane Database Syst Rev. 2005

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Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

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