St. John's Wort in pregnancy and breastfeeding

What NCCIH says about safety

For most adults who are not taking any kind of medicine, St. John’s wort appears to be safe when used for up to 12 weeks, and some studies indicate that it can be used safely for a year or more. If taken orally in large doses or applied to the skin, St. John’s wort might cause severe skin reactions after sun exposure. Other side effects can include diarrhea, dizziness, trouble sleeping, restlessness, and skin tingling. If you take any type of medicine, talk with your health care provider before using St. John’s wort or other herbal products; some herbs and medicines interact in harmful ways. For example, St. John’s wort can weaken the effects of many medicines, including crucially important medicines such as: Some antidepressants, including amitriptyline and bupropion Birth control pills Cyclosporine, which prevents the body from rejecting transplanted organs Some drugs used to prevent seizures, including phenytoin and carbamazepine Some heart medications, including digoxin and ivabradine Some HIV drugs, including indinavir and nevirapine Some cancer medications, including irinotecan, imatinib, and docetaxel Warfarin, an anticoagulant (blood thinner) Certain statins, including simvastatin In addition, taking St. John’s wort with certain antidepressants or other drugs that affect serotonin (a substance produced by some nerve cells) may lead to increased serotonin-related side effects, which can be serious. It may be unsafe to use St. John’s wort during pregnancy because it may increase the risk of birth defects. Breastfeeding infants of mothers who take St. John’s wort can experience colic, drowsiness, and lethargy.

Quoted in full from NCCIH so nothing is lost in summarising. Where they say “little is known”, that means the studies do not exist — not that the herb is known to be safe, and not that it is known to be harmful.

How much is actually known

Many studies have been done on the usefulness of St. John’s wort for depression, and their results indicate that it may be helpful for mild or moderate depression. For other conditions, the evidence is insufficient to allow definite conclusions about the usefulness of St. John’s wort to be reached. It has been clearly shown that St. John’s wort can interact in dangerous, sometimes life-threatening ways with a variety of medicines.

What the research has found

St. John’s wort appears to be more effective than a placebo (an inactive substance) and as effective as standard antidepressant medications for mild or moderate depression. It’s uncertain whether this is true for severe depression or for time periods longer than 12 weeks. Small numbers of studies suggest that St. John’s wort may be helpful for hot flashes associated with menopause and for somatic symptom disorder (a condition involving intense anxiety about physical symptoms). St. John’s wort has also been studied as a treatment for a variety of other conditions, including attention-deficit hyperactivity disorder (ADHD), irritable bowel syndrome, obsessive compulsive disorder, and premenstrual syndrome; as a possible aid to smoking cessation; and as an ingredient in topical preparations for wound healing. However, only a small amount of research has been done on the use of St. John’s wort for each of these purposes, and the evidence hasn’t clearly shown it to be helpful for any of them.

Before you take this

Dose and form change the answer completely. A culinary amount of a spice, a cup of tea, and a concentrated supplement extract are three different things, and most research is done on the last of them.

Supplements are also not regulated like medicines, so strength and purity vary between products. Bring the actual bottle to your midwife, doctor or pharmacist — that conversation is worth more than any page, including this one.