Cautions & Contraindications

Cautions, Contraindications, Side-Effects and InteractionsAny information given in this website does not remove the requirement to consult a professional medical practitioner, whether a GP, herbalist or homeopath

It is important to know what the cautions, contra-indications, side-effects and interactions are for herbal medicines. This section should help you understand what these terms mean, and give some examples of the cautions, contra-indications, side-effects and interactions for different herbs, vitamins and minerals.

Herbs are considered by many to be “perfectly safe”, because they are natural. While we believe that herbal medicines are safer than many medicines that originate from a laboratory, this is only true if they are used appropriately. Inappropriate use of some herbs could be dangerous, this includes combining them with prescription medicines or using them to treat serious illness without the help of a professional.

This section will highlight some of the key factors to consider, and also some of the herbs that are known to have contraindications or interactions with prescription medicines. Information is constantly being updated as new research is published, therefore this information cannot be considered as definitive.

A remedy’s contraindications let you know when it is unsuitable to be used. Contraindications may include pregnancy, meaning the product should not be used during pregnancy, or a particular medicine, such as aspirin which should not be combined with some herbs.
A caution means that it is possible that the remedy may not be recommended in some circumstances, it is not as strong as a contraindication. Cautions include the fact that some herbs may irritate the stomach. It is up to the individual to decide if they mind the possibility of that side effect.
Side Effects
Side effects of a medicine are effects which may occur to the body due to taking the medicine, in addition to the desired effect. Side effects may include effects that are seen in most people taking that medicine, or side effects that may have occurred only once!
An interaction occurs when the administration of one medication (whether herbal or not) affects the action of another medication. These interactions can occur either by one medication directly acting on the other, or through their effects on the human body. For example the herb St John’s Wort (Hypericum perforatum) causes one of the processes in the liver (the P450 enzyme system) to be more efficient. Whilst this is not normally considered an issue in a healthy person not taking any medication, it does cause some drugs that are metabolised by the liver to be removed from the body more quickly – meaning that they would no longer be as effective. This includes the contraceptive pill!

General Considerations

In general, the key thing to consider is that if you are deciding to use herbal medication, vitamins and minerals by yourself then you are responsible for your own healthcare! If you are unsure then it is almost certainly worth obtaining the assistance of a medical professional. The following list indicates when you should be especially careful when using herbal remedies or vitamins and supplements.

  • Where the patient is young (i.e. from infant to approximately 11 years old)
  • If you are taking any prescription medicines
  • If you are treating a significant health complaint
  • If you are normally sensitive or allergic to substances.
  • If you do not have a diagnosis of what is wrong with you from a medical professional


During pregnancy and breastfeeding professional advice is essential. See our page on Pregnancy and Fertility for more information.

Some Examples of Cautions and Contraindication

Knowledge of Herbal Medicine and the human body is growing all the time and as a result knowledge of the effects of different herbs and their constituents continues to develop. Advice may come from many different sources: purely theoretical considerations; the observed effects of the herb on patients through time, passed down through the oral tradition; or modern studies on patients, ranging from results of a large clinical trials to a single case studies.



Cautions and Contraindications of Some Herbs

St John’s Wort (Hypericum perforatum)

Contraindications: Pregnancy due to its ability to stimulate the uterus, and if breastfeeding.

If you are taking conventional anti-depressants or are suffering from severe depression.

Cautions: It is recommended that foods containing tyramine, such as cheese, wine, yeast and beer, are avoided whilst taking St. John’s Wort.

If you are HIV positive and receiving treatment it is recommended that you consult a qualified medical practitioner before taking St. John’s Wort.

Side-effects: Some individuals with fair skin have experienced an increased sensitivity to the sun whilst taking St. John’s Wort. It is therefore recommended that you avoid excessive amounts of sun exposure and wear a good quality sunscreen (as you should do anyway!) if you anticipate being exposed to the sun for long periods of time.

Interactions: St John’s Wort affects the function of a group of liver enzymes termed the Cytochrome P450 enzymes, and can therefore affect the metabolism of a variety of drugs by either clearing them more quickly or slowly from the body. This is of particular importance if you are taking the contraceptive pill, anti-coagulants (such as warfarin), digoxin, cyclosporine, theophylline tablets for asthma or chronic bronchitis, statin drugs, protease inhibitors, e.g. Indinavir, or medication for epilepsy or migraines as the herb may stop them from working properly.

Raspberry Leaf (Rubus idaeus)

Contraindications: Raspberry leaf is contraindicated in pregnancy, if the pregnant lady has a history of rapid labour.

Cautions: Raspberry leaf tea should be taken as a tea only during the last trimester of pregnancy (Week 28-36 and onwards).

Gingko Biloba

Contraindications: Ginko biloba is contraindicated if you are undergoing surgery. You should stop taking the herb at least 7 days prior to any surgery.

Interactions: Ginko biloba should not be used if aspirin or warfarin are being taken.

Cautions and Contraindications of Some Vitamins

Vitamin A

Contraindications: Vitamin A supplementation is contraindicated if you are pregnant, or are likely to become pregnant, except on the advice of a qualified medical practitioner.

Cautions: Excessive supplementation with Vitamin A over extended periods of time can lead to toxicity as the vitamin is stored in the liver.

Vitamin B6

Cautions: Long-term daily intake of 500mg or a shorter-term daily intake of 2000mg vitamin B6 has been shown to cause nerve toxicity in some people.

Interactions: Supplementation with vitamin B6 should be avoided if you are taking Levodopa for Parkinson’s Disease.

Vitamin D

Cautions: Vitamin D can also cause toxicity if taken for an extended period of time. It is therefore important that daily intake does not exceed 25µg (1000iu). (This includes Vitamin D from food sources).

Interactions: Vitamin D supplementation should not be taken if you are taking digoxin, thiazide diuretics, or calcitonin, unless supervised by a qualified medical practitioner.

Vitamin E

Contraindications: High doses of vitamin E are contraindicated prior to surgery or going into labour due to its anti-clotting effects.

Interactions: High doses of vitamin E should not be taken in combination with anti-coagulant drugs such as warfarin, aspirin or heparin as it may enhance their effects.

PABA (Para-aminobenzoic acid)

Interactions: PABA should not be taken at the same time as the sulfa-class of antibiotics (e.g. sulphadimidine, sulphadiazine) as it may interfere with their action.

Cautions and Contraindications of Some Minerals


Contraindications:Those with cancer or hyper-parathyroid disorder should not take calcium supplements.

Interactions:Calcium supplements should not be taken if you are taking blood pressure lowering drugs, digoxin or tamoxifen. Calcium may decrease the absorption of certain other drugs and should therefore be taken at least 2 hours away from taking other drugs.


Interactions:Zinc supplementation should be avoided if taking amiloride, penicillamine, tetracycline, warfarin or fluoroquinolone antibiotics (e.g.ciprofloxacin).

Cautions and Contraindications of Some Food Supplements

Evening Primrose Oil

Contraindications:Evening primrose oil should be avoided if you have epilepsy.

Side Effects:May cause headaches, nausea, or skin eruptions. These effects may be lessened by taking with food.

Interactions:It is recommmended that evening primrose oil is not taken in combination with drugs for schizophrenia.

Fish Oils

Side-effects:Nausea may be experienced if taking fish oils for the first time. This tends to ease off with time and can be lessened by taking with food.

Interactions:High doses of fish oils should be avoided if you are taking blood-thinning drugs such as heparin or warfarin.

Cautions and Contraindications of Some Essential Oils

Although essential oils are not taken internally, they are readily absorbed by the body and because they do not go straight to the liver after absorption (as is the case for food or any drugs consumed orally) they are delivered directly to the bloodstream. This means that essential oils should be treated with caution.

The main ways in which essential oils are used are:

  • dermal – applied to the skin either by massage or by placing the oil in the bath
  • inhalational – breathed in and absorbed by the respiratory tract and lungs
  • (techniques that should only be followed with professional advice are are oral, rectal and vaginal)

Examples of oils that should not be used in specific circumstance include

  • Some oils are irritant to skin and are not recommended for damaged, diseased or hypersensitive skin (e.g. Citronella, Melissa, Thyme)
  • avoiding Ho Leaf, Camphor (White), Hyssop (and others) in anyone suspected of being vulnerable to epileptic seizures
  • caution requied with Indian Dill, Parsely leaf and Parsely seed in kidney disease