Herbal Medicines: Why Herbal Does Not Mean Harmless

St John’s wort for your mood, valerian to help you fall asleep, ginkgo for your memory — herbal remedies are seen as gentle and natural. But “natural” is no promise of safety: plant extracts are mixtures of many active substances, and some of them can markedly change the effect of other medicines. St John’s wort, for example, can weaken the pill or anticoagulants. This guide shows you which plants call for particular caution, how to recognise tested products and how to combine them safely with the rest of your medication.

1. What herbal medicines are — and what they are not

Herbal medicines (phytopharmaceuticals) contain plants, parts of plants or preparations made from them as their active ingredient — such as extracts, essential oils, tinctures or teas. They work on the same principles as other medicines: through constituents that are absorbed by the body and act there on enzymes, receptors or transporters. This leads to a simple rule: anything that can have an effect can also have side effects and interactions.

Two distinctions are important:

• Homeopathy is not herbal medicine. Although some homeopathic remedies are made from plants, they follow a different principle and are usually so highly diluted that little or none of the original substance remains. They are not the subject of this guide.
• Vitamins and minerals are a separate topic. Which nutrient supplements are compatible with medicines is explained in the guide Supplements and medications. This article focuses on remedies made from plants.

2. Authorised, registered or food supplement: the crucial difference

Herbal products that have been tested to very different degrees stand side by side on the market. For you, this is the most important point when buying, because it determines what you actually know about effectiveness and quality.^¹,²

At European level, the European Medicines Agency’s Committee on Herbal Medicinal Products (HMPC) assesses the evidence on individual medicinal plants in what are known as monographs. These record whether a use is considered “well-established” or only “traditional” — and which contraindications, warnings and interactions are known.^²

3. St John’s wort: the prime example of interactions

St John’s wort is the best-known example of how herbal products can have serious consequences — and at the same time one of the best-studied phytopharmaceuticals. The German National Disease Management Guideline on unipolar depression names St John’s wort extracts as a possible option for mild to moderate depressive episodes, but explicitly points out the interactions and the varying quality of the products.^³ Products authorised for treating moderate depression are prescription-only in Germany; lower-dose remedies for mild, temporary low mood are available without a prescription at the pharmacy. You can find more about the condition itself in the article Depression.

Why St John’s wort weakens so many medicines

Constituents of St John’s wort — above all hyperforin — stimulate certain breakdown enzymes (especially CYP3A4) and the transport protein P-glycoprotein in the liver and gut. The result: many other active substances are broken down faster or absorbed less well, their level in the blood falls and their effect wears off. This effect builds up over a few days and persists for about one to two weeks after stopping.^⁴

For contraception, the rule is: while you are taking St John’s wort and for some time afterwards, an additional barrier method such as condoms is needed — exactly how long is stated in the summary of product characteristics of the contraceptive concerned. The guide Medications and contraception explains the background. St John’s wort can also make the skin more sensitive to light — a topic for the summer, see Medications and sun.

4. Other plants you should keep an eye on

St John’s wort is the best-known case, but not the only one. The following overview lists commonly used plants with known or suspected risks. For some of them the evidence is thin — but that does not mean there is no risk, only that it has been less well studied.

An honest assessment of effectiveness is also part of the picture: for valerian and other herbal sleep aids, the guideline on the treatment of sleep disorders considers the evidence insufficient for a recommendation.^⁵ That does not make them dangerous, but it puts their benefit into perspective. What really helps with sleep problems is described in the guide Sleeping pills: what really helps?. And if you take calming herbal remedies, you should know the advice on medications and driving.

5. Hidden risks: contamination, imports, miracle cures

Besides the active substances themselves, there are risks that have to do with manufacturing and origin. For authorised and registered medicines, quality and purity are regulated by the authorities; for food supplements and imported goods, this is much less assured.

• Pyrrolizidine alkaloids: these natural plant toxins can damage the liver if taken in over a longer period. They occur in some medicinal plants such as comfrey, coltsfoot or butterbur — which is why only specially processed products are available for internal use. They also get into herbal and medicinal teas as contamination from weeds harvested along with the crop. The German Federal Institute for Risk Assessment (BfR) has repeatedly pointed this out and advises, among other things, varying the teas you drink.^⁶
• Imported products: in remedies bought online or abroad, for example from traditional Chinese or Ayurvedic medicine, heavy metals, kidney-damaging plant components such as aristolochic acids or undeclared pharmaceutical substances have repeatedly been found.
• Red yeast rice: advertised as a food supplement for raised blood lipids, it contains monacolin K — chemically identical to the cholesterol-lowering drug lovastatin. It therefore brings with it the typical statin side effects such as muscle complaints, as well as the corresponding interactions. The EU has limited the permitted amount. The guide Lowering cholesterol shows proven ways to improve your blood lipids.
• Miracle cure promises: products that claim to help against “everything”, promise rapid weight loss or claim to cure serious illnesses are a warning sign — such promises are not allowed for authorised medicines.

6. Particular caution: pregnancy, children, surgery, pre-existing conditions

Pregnancy and breastfeeding

For most herbal remedies there are no reliable data on use during pregnancy and breastfeeding — “traditionally used” is no proof of safety for the unborn child. On top of that, many tinctures and drops contain alcohol. So ask at your practice or pharmacy before using anything. The Embryotox advice centre at the Charité in Berlin provides independent information on individual active substances.^⁷

Children

Many herbal medicines have not been adequately studied in children under twelve or are not approved for them. Drops containing alcohol are unsuitable for children, and essential oils such as camphor, menthol or eucalyptus oil must not be used on the face of babies and young children — they can trigger a dangerous spasm of the larynx. More in the guide Children and medications.

Before surgery

Herbal remedies belong in every pre-anaesthetic consultation. Ginkgo, high-dose garlic and other remedies with a possible effect on blood clotting, as well as St John’s wort because of its interactions, are often paused before a procedure — when and for how long is decided by the treatment team. Further advice in the guide Medications before surgery.

Chronic illnesses and long-term medication

• Liver and kidney disease: some plants put an additional strain on these organs; taking them should be agreed with your doctor.
• After organ transplantation and during HIV treatment: St John’s wort is practically always off-limits here; other remedies only after consultation too.
• Blood thinning: discuss every new herbal remedy with your practice or pharmacy beforehand.
• Allergies to the daisy family: chamomile, arnica, marigold and purple coneflower can trigger reactions.

7. Where herbal remedies can make sense — an honest assessment

Herbal medicines are not inherently worse or better than others. What matters is how well the specific product has been studied. A rough classification:

• Comparatively well studied — for example certain St John’s wort extracts for mild to moderate depression, peppermint oil capsules for irritable bowel symptoms or psyllium husks for constipation. Here too: only standardised products at a tested dose.
• Limited or conflicting evidence — such as valerian for sleep disorders or purple coneflower for preventing and treating colds. A trial may be justifiable; high expectations are not.
• Hardly any evidence of benefit — for example saw palmetto extract for complaints caused by an enlarged prostate, which in larger studies did no better than a placebo. More about the condition in the article Prostate enlargement.

The message is not “hands off”, but: treat herbal remedies as seriously as any other medicine. Whether a herbal product fits into your treatment is best decided together with your practice — especially if it is meant to supplement or replace a prescribed treatment.

8. Step by step: using herbal remedies safely

1. Clarify the complaint. With new, persistent or worsening complaints, have them assessed by a doctor first — herbal remedies do not replace a diagnosis.
2. Choose a tested product. Ideally a medicine with an authorisation or registration number from the pharmacy, with a defined dose and a package leaflet.
3. Have interactions checked. At the pharmacy, name all the medicines you take — especially anticoagulants, hormonal products, antidepressants, and heart and immune medicines.
4. Stick to the dose and duration. The package leaflet states how long a remedy should be used without medical advice. “More” or “longer” is no more harmless with plants than with other medicines.
5. Document it. Enter the remedy in your medication plan and mention it at every visit to the doctor or dentist.
6. Watch the effect. Decide beforehand how you would recognise a benefit and after how long you will take stock. If there is no effect, there is no reason to carry on.
7. Stop with a plan. If you want to stop St John’s wort or another remedy with many interactions while taking finely adjusted medicines, tell your practice first — the levels of the other active substances may change.

Which other foods and combinations affect how medicines are broken down is shown in the guide Avoiding drug interactions.

9. How brite helps you with herbal medicines

Herbal remedies, clearly tracked — with brite

All your remedies in one plan, interactions checked, effects documented. Free of charge.

Start for free