Carusos St Johns Wort

St John's wort is one of the best-researched herbs there is, and it's also one where what else you take matters more than the herb itself. These are the questions our naturopaths ask in store.

A good fit if

• You're an adult and you take no prescription medicines at all
• You want a standardised, quantified extract rather than loose herb or powder
• You've read the label warning and know to mention it to any doctor treating you
• You're happy to check in with a naturopath if your circumstances change

Check with us first if

• You're on the contraceptive pill. It's named in the label warning and in the interaction research.
• You take an antidepressant or another medicine that acts on serotonin. Several are on the interaction list, and combining mood medicines needs your doctor's input.
• You're having surgery. Anaesthetics and related drugs are named in the interaction research, so tell your anaesthetist.
• You take warfarin. A dedicated review found St John's wort changes warfarin levels in your blood.
• You take anti-rejection medicine after a transplant, such as ciclosporin or tacrolimus. If those levels fall, there's a risk of rejection.
• You take HIV medicines. A review found important changes in drug levels when the two are combined.
• You take a statin, digoxin, methadone or a cancer medicine such as imatinib or irinotecan. All are named in the interaction research.
• You take any prescription medicine at all, even one not listed here. A published review names more than 45 affected drugs in total.
• If you take prescription medicines, check with your doctor, pharmacist or our naturopaths before you start.

• Standardised dried alcoholic extract, quantified (item 4721). Best known for: The extract almost every clinical trial used. Absorption: Standardised to a set hypericin and hyperforin content, so the active dose is stated. Typical use: Tablets and capsules; this is the form the evidence here is about.
• Herb dry (item 4722). Best known for: The whole dried herb. It's allowed, but it isn't what trials used. Absorption: Its content isn't standardised the way the quantified extract is. Typical use: Capsules and loose herb; the same compulsory warning applies.
• Herb powder (item 4723). Best known for: Ground dried herb, again not what trials used. Absorption: Not standardised to hypericin or hyperforin content. Typical use: Capsules and powders; the same compulsory warning applies.
• Hypericum perforatum as a botanical ingredient (item 2672). Best known for: The species itself, covering any preparation not covered by the other three entries. Absorption: Depends entirely on how it's prepared. Typical use: Any form taken by mouth; the same compulsory warning applies.
• Tea or water infusion. Best known for: A common home preparation, but not a tested one. Absorption: There's no trial of a water infusion, and hyperforin dissolves poorly in water. Typical use: It would come under the herb dry or herb powder rules; the clinical evidence doesn't apply to it.
• Hypericum ascyron or Hypericum japonicum (items 2670, 2671). Best known for: Different species entirely, despite the similar name. Absorption: Not applicable. None of the St John's wort evidence applies to them. Typical use: Allowed with no warning at all, so check the label names the right species.

Reference values. None. St John's wort is a herb, not an essential nutrient, so the NHMRC sets no recommended intake or upper limit for it.

Typical supplemental range. The systematic reviews behind this page don't state doses. The one figure we have is how the extract is standardised, commonly 0.3% hypericin and 1 to 4% hyperforin, and studies most often ran for 4 to 12 weeks.

Upper level. There's no NHMRC upper limit, and Australian rules set no daily dose cap on any St John's wort ingredient. The conditions attached to it are all about drug interactions, not how much you take.

Worth knowing. There's no long-term safety or dosing data beyond about 12 weeks, which matters for a herb some people take for months or years. What you need depends on your age, diet and health, so talk to one of our naturopaths.

If any of these sound like you, talk to one of our naturopaths or your doctor before you start.

• Any prescription medicine. The compulsory label warning says it can change how many medicines work, including the pill.
• The contraceptive pill in particular. It's named in the label warning and in the interaction research. The risk is an unplanned pregnancy.
• Anti-rejection medicines after a transplant, such as ciclosporin and tacrolimus. Falling blood levels risk rejection of the transplant.
• HIV (antiretroviral) medicines. Important changes in drug levels have been reported.
• Warfarin. A dedicated review found it affects warfarin's blood levels.
• Antidepressants and other medicines that act on serotonin. They're on the interaction list; combining them needs medical advice.
• Anaesthetics and surgery. Tell your anaesthetist beforehand.
• Cancer medicines such as imatinib and irinotecan. These are named in clinical trial interaction data.
• Pregnancy and breastfeeding. We found no safety data either way.
• Children. We found no data in children.
• Ongoing low mood that isn't improving, or thoughts of self-harm. See a doctor, not a supplement.
• Long-term use. Trials ran for only 4 to 12 weeks, and there's no longer-term data.
• A different species sold under a similar name, such as Hypericum ascyron or Hypericum japonicum. It isn't the same herb, and none of the cautions or evidence here apply to it.
• If you take prescription medicines, check with your doctor, pharmacist or one of our naturopaths before you start.