Can some supplements stop medicines from working?

Supplements will not generally stop medicines from working. However, there are interactions between nutritional status and the action of some medicines.

Certain medicines influence the absorption or metabolism of some nutrients. For example, some anti-ulcer agents reduce the absorption of vitamin B12 and the anticonvulsant drug phenytoin increases the breakdown of folic acid.

Conversely, certain nutrients may influence the action of medicines; vitamin K reduces the clotting effect of the blood which means that the effects of anti-coagulant medications like warfarin will be increased leading to a greater risk of bleeding.

In addition, some herbal remedies may influence the efficacy or toxicity of some prescription medicines; for example St. John’s Wort (hypericum) reduces the efficacy of the contraceptive pill.

People should always read the product indications carefully before taking a supplement, and if still uncertain, consult a pharmacist or the doctor who has prescribed the medicine.

µg	Microgram a measurement of weight equal to one millionth of a gram (or one thousandth of a milligram). Microgram (µg or mcg) is used for a number of nutrients found in food supplements.
Amino Acid	The building blocks of protein, there are eight essential amino acids which cannot be synthesised within the body and therefore must come from the diet. These are: isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. In addition arginine and histidine are amino acids required by infants and young children which supports their rapid growth.
Antioxidant	A substance or nutrient which helps to protect our cells from damage caused by free radicals, damaging molecules which are found in pollution and tobacco smoke. Our bodies also produce free radicals as part of the normal biochemistry of living.
Deficiency	A lack of essential macronutrients or micronutrients which results in malnutrition and or disease. This may be the result of inadequate intakes or absorption issues associated with gastrointestinal disease. There are a number of recognised deficiency diseases including (but not exclusively): scurvy (vitamin C deficiency); rickets (vitamin D deficiency); anaemia (iron deficiency, but also deficiencies in B12 and folic acid) and Kwashiorkor (protein deficiency).
DH	The Department of Health is a UK Government department. It has responsibility for nutrition legislation and sets health policy for nutrition.
DHA	Docosahexaenoic acid; one of the key omega-3 fats that provides health benefits
Dietitian	An individual qualified in nutrition and dietetics who can assess, diagnose and treat health issues associated with nutrition and diet. Dietitians are governed by law with a statutory code of practice; they often work within the health service although increasing numbers are also working in a freelance capacity.
EFA	Essential fatty acids (omega 3 and omega 6) cannot be synthesised by the body and must be derived from the diet. EFAs do not provide fuel for energy production and are required for vital biological processes which support growth, development and health.
EFSA	European Food Safety Authority; the European Union food risk management agency which scientifically evaluates safety across all areas of food.
EPA	Eicosapentaenoic acid; one of the key omega-3 fats that provides health benefits.
Fat soluble vitamin	The fat soluble vitamins are vitamins A, D, E and K. Because they are fat soluble these substances can accumulate in the body, often being stored in fat cells, or in the liver. This can create health issues, particularly if intakes have been high for a prolonged period of time. For example, long term high intakes of vitamin D may lead to the laying down of calcium in tissues such as liver and kidneys which can cause nausea and vomiting.
Food supplement	A food supplement is a concentrated source of vitamins, minerals or other substances with a nutritional or physiological effect which is sold in small, measured unit doses.
FSA	The Food Standards Agency is a non-ministerial UK Government department responsible for food safety and food hygiene.
GLA	Gamma-linoleic acid is an omega-6 fatty acid (an essential fatty acid considered to be necessary for human health which must be derived from the diet). GLA is most commonly found in evening primrose oil (EPO), borage or starflower oil and blackcurrant seed oil.
Health claim	A health claim is any claim which states, or implies, that consumption of a specific food will have a beneficial effect on health. Claims may be written, verbal or pictorial.
Herbal medicine (herbal remedy)	A product is considered to be a herbal medicine if the main active ingredient/s are only herbal substances or preparations. Not all herbal products are medicines, some may be food supplements and some may be cosmetics. What determines if a product is, or is not a medicine is complex but generally rests with how the product is presented (i.e. does it make medicinal claims to treat, prevent or cure any disease) and what it does (i.e. does it have a physiological impact on, or alter, any body functions).
Macronutrient	Dietary constituents which are needed in significant amounts, generally protein, fat, carbohydrate, fibre and water.
Malnutrition	Malnutrition is a state in which the deficiency of nutrients such as energy, protein, vitamins or minerals results in measurable adverse effects on the body. Malnutrition may refer to insufficient intake of protein, carbohydrate and fats (macronutrients) which can result in overly low BMI. It may also be insufficient intake of vitamins, minerals and other micronutrients, which can impact on overall health and could include obese individuals with poor diets.
Mg	Milligram is a measurement of weight equal to one thousandth of a gram. Mg is used for a number of nutrients found in food supplements.
Micronutrient	A substance derived from food which is needed in extremely small amounts for the normal growth and development of living beings. Micronutrients are vitamins, minerals and essential fatty acids (omega-3 fats)
Mineral	Inorganic micronutrient essential to health and wellbeing. Minerals are absorbed from soil by plants which are in turn eaten by animals or humans. Minerals may be split into minerals which are needed in relatively high amounts (calcium, phosphorus, magnesium, sodium, chloride and potassium) and trace elements (iron, zinc, cobalt, copper, chromium, fluoride, iodine, manganese, molybdenum, boron and selenium) which are needed in very small quantities.
Multivitamin	A product which contains more than one vitamin, often multivitamins will contain all 13 vitamins although some may contain only the eight B vitamins, or a combination of some of the vitamins and some additional minerals.
NDNS	The UK National Diet and Nutrition Survey is a continuous rolling survey of the dietary habits and nutritional status of adults and children in the UK. The results are used to assess whether intakes of food and nutrients are adequate across different ages and population groups.
NRV	Nutrient Reference Value is the amount set by the European Food Safety Authority (EFSA), primarily to support food labelling, which the majority of the population requires to maintain health. Previously known as RDA
Nutrient	A substance derived from food which provides nourishment to the body and is essential for the maintenance of life and for growth and development.
Nutritionist	Nutritionists generally work for public bodies or governments, although some do work with private clients. They tend to look at large populations to determine risk factors and make dietary recommendations that are applied at population levels. For example, evidence on the incidence of type II Diabetes led public health nutritionists to determine that some populations are more at risk of developing this disease, and to make recommendations for dietary changes to either reduce the risk or manage the disease. However, public health nutritionists do not practice with individual patients.
Omega-3 fats	Essential fatty acids which cannot be synthesised by the body and must be derived from the diet. Primary sources for omega-3 fats are oily fish and fish oil supplements with some also coming from enriched eggs and fortified foods. There are a number of scientifically proven health benefits for omega-3 fats including supporting the health of the eyes, brain and heart, maintaining an appropriate balance of triglycerides in the blood and reducing blood pressure.
Omega-6 fats	Essential fatty acids which cannot be synthesised by the body and must be derived from the diet. Primary sources for omega-6 are vegetable oils such as sunflower and corn oils as well as nuts and seeds. There are a number of health benefits associated with omega-6 fatty acids; they are thought to be beneficial in the management of premenstrual syndrome and in some skin conditions including eczema and psoriasis.
PAGB	Proprietary Association of Great Britain (PAGB) is the UK trade association which represents the manufacturers of branded over-the-counter medicines, self care medical devices and food supplements.
Prebiotics	Foods which promote the growth of probiotics, the beneficial bacteria that inhabit our gut. Prebiotics are generally fibres such as inulin, which our bodies cannot digest and absorb but which provide a food source for probiotics.
Probiotics	Live bacteria (and some yeasts) which inhabit the digestive tract which are viewed as being beneficial to human health. There are thousands of different bacterial strains; some are resident in specific areas of the digestive tract whilst others are transient, simply passing through.
Public Health England (PHE)	Public Health England is an agency of the Department of Health responsible for improving public health. They work with local government, the NHS and non-governmental organisations as well as communicating public health messages to the general public.
PUFA	Polyunsaturated fatty acids (PUFA) are found in nuts, seeds, fish (and fish oil), krill and some algae, small amounts are also found in leafy greens. The omega-3 and omega 6 fats are PUFAs, which are generally associated with health.
RDA	Recommended Daily Amount; previously used terminology for the amount set, primarily to support food labelling, which the majority of the population require to maintain health. Now described using nutrient reference value (NRV)
SUL	Safe Upper Levels of vitamins and minerals were established by the Expert Group on Vitamins and Minerals who published a report in 2003 (https://cot.food.gov.uk/sites/default/files/cot/vitmin2003.pdf). The UK food supplements industry works to the levels set in this report.
Vitamin	Organic micronutrient essential to health and wellbeing. Vitamins cannot be synthesised in sufficient amounts by the animal or human body and must therefore be obtained from the diet. Plants manufacture vitamins which move up the food chain as the plants are consumed by animals or humans. Vitamins can be divided into fat soluble (vitamins A, D, E and K) and water soluble (vitamins B1, B2, B3, B5, B6, B12, biotin, folic acid and vitamin C).
Water soluble vitamin	The B vitamins and vitamin C are water soluble. They are not stored in any significant quantities within the body and are generally either utilised or excreted in the urine. As they are not stored in the body, they tend to have low toxicity and are needed on a daily basis.