Interactions Between Medications and Supplements

Interactions Between Prescribed Medications and Supplements

Mar 03, 2023

Supplements are used to aid a healthy diet and balanced lifestyle, to help keep the body functioning as it should be. Deficiency in any vitamin/mineral, can cause problems which can develop into serious health conditions. Prescription medication is a form of treatment option, after the health condition has already been developed.  


Prescribed medication (NHS prescriptions) has an intended effect on the body. When combined with certain vitamins and minerals, which contribute to the same intended/opposite effect, may cause an unwanted reaction/adverse effect. Below is a list of known interactions between medications and supplements. These are interactions that may happen as everyone is different, and diet and lifestyle factors vary greatly. Separating your medication and supplement intake by two hours, should minimise any side effects. If you think you are having a reaction, stop taking the supplement/naturally occurring food sources and contact your doctor. 


Interactions Between Medications and Supplements


Vitamin A 

  • Weight loss drugs such as Orlistat can decrease the absorption of Vitamin A and other fat-soluble vitamins (D, E & K). This can lead to a decreased plasma level. 
  • Retinoids, typically used for the treatment of skin problems, when combined with Beta Carotene supplements may cause overdose.

Vitamin B1 

  • Furosemide is used to treat oedema and hypertension and is a diuretic. It can cause deficiency in Thiamine (Vitamin B1) as it is water-soluble, so it is excreted in our urine.

Vitamin B3 

  • Tuberculosis medication, such as Rifater is structurally similar to Niacin (Vitamin B3) and therefore, disrupts the conversion of Niacin and production of tryptophan
  • Large doses of Niacin have been linked to an increase in blood glucose levels. Therefore, individuals on diabetic drugs and taking Vitamin B3 should regularly monitor their blood glucose levels.

Vitamin B7 

  • Studies have found that taking anticonvulsants can decrease serum Biotin (Vitamin B7) levels as they can increase Biotin breakdown and inhibit absorption.

Folic Acid 

  • Folic Acid (Vitamin B9) interacts with the anticancer effects of high doses of Methotrexate. However low doses of B9, used to treat rheumatoid arthritis or psoriasis may help reduce gastrointestinal side effects of methotrexate.
  • Antiepileptic medications interact negatively with Folic Acid supplements, as they may reduce their effectiveness.
  • Sulfasalazine, commonly used to treat ulcerative colitis inhibits the absorption of Folic Acid which may cause deficiency.

Vitamin B12 

  • Gastric acid inhibitors such as Omeprazole/Lansoprazole known to slow the release of gastric acid into the stomach, can interfere with Vitamin B12 absorption, causing deficiency.
  • Absorption can also be prevented by diabetic medications such as Metformin

Vitamin C 

  • There have been many studies investigating the effects of Vitamin C supplementation, alongside chemotherapy/radiation for the treatment of cancer. As Vitamin C contributes to the protection of cells from oxidative stress (antioxidant) it is thought that it may provide some “non-cancerous cells” with protection from the harsh treatment. But this has not been confirmed.

Vitamin D 

  • Orlistat, a weight loss drug when taken in combination with a reduced fat diet can obstruct the absorption of Vitamin D.
  • Vitamin D is produced from cholesterol, Statins, used to reduce cholesterol levels in the body, may lower Vitamin D levels. Vitamin D and statins compete for the same metabolic enzyme, which may affect the ability of the statins to lower cholesterol levels.
  • Vitamin D metabolism is also impaired by Corticosteroid drugs, prescribed to reduce inflammation.
  • Thiazide Diuretics and supplemental Vitamin D may lead to hypercalcemia as these two combined, can cause an increase in calcium absorption.

Vitamin E 

  • Vitamin E has blood thinning properties, taken with Anticoagulant and Antiplatelet drugs, such as Warfarin, can increase the risk of bleeding from blood vessels.
  • Sources of Vitamin E combined with other antioxidants (Selenium, Beta Carotene) slows the rise in HDL cholesterol (“good cholesterol”) in those being treated with Simvastatin.
  • As discussed earlier, antioxidants have been investigated in their ability to protect “non-cancerous” cells from chemotherapy/radiotherapy, however, some believe that antioxidants may protect the “cancerous” cells, defeating the purpose of treatment.

Vitamin K 

  • Vitamin K has blood clotting properties, which may interact with Anticoagulant and Antiplatelet drugs (Warfarin).
  • Antibiotics destroy the good bacteria within the gut, which can reduce Vitamin K concentration, leading to deficiency.
  • Cholesterol lowering (bile acid sequestrants) drugs can affect the amount of Vitamin K the body absorbs.
  • Weight loss medication reduces the amount of fat absorbed by the body, influencing Vitamin K levels.


  • Magnesium may affect the function of Oral bisphosphonates typically used to treat osteoporosis.
  • Tetracycline antibiotics should be taken two hours before or 4-6 hours after Magnesium to avoid interference.
  • Loop and thiazide diuretics can increase the loss of Magnesium through urine output, whereas potassium sparing diuretics reduce Magnesium excretion.
  • Magnesium should be taken by individuals on proton pump inhibitors as they have been known to lower Magnesium serum levels.


  • The effectiveness of Levodopa is reduced when taken with Iron. Levodopa is used to treat Parkinson's disease and restless leg syndrome. 
  • Iron supplements can also have an impact on the function of Levothyroxine (hypothyroidism and thyroid cancer medication).
  • Individuals who take proton pump inhibitors, for example, lansoprazole and omeprazole can find it difficult to absorb Iron, leading to deficiency.


  • Zinc may interreact with Quinoline and Tetracycline antibiotics, resulting in a decreased absorption in both.
  • Drugs used to treat rheumatoid arthritis and Wilson disease (Penicillamine) can interact with Zinc.
  • Zinc deficiency can be caused by Thiazide diuretics as Zinc is excreted in our urine.


  • Calcium can affect the function of Dolutegravir, a HIV inhibitor. 
  • Levothyroxine, commonly used to treat hypothyroidism and thyroid cancer combined with Calcium may affect the absorption of levothyroxine.
  • Typical treatment of bipolar involves Lithium. Lithium can lead to hypercalcemia, taking both together may increase the risk and severity of hypercalcemia.
  • Concurrent intake of Calcium and Quinoline antibiotics can decrease the absorption of the antibiotics.
  • There is a possibility that Calcium absorption is hindered by Corticosteroid medications.


  • Those who take Insulin and antidiabetic medications such as Metformin, should be wary of Chromium supplements as it may increase insulin sensitivity and lower blood sugar levels.
  • The absorption of Levothyroxine can be reduced by Chromium.


  • Some studies have shown simultaneous intake of Cisplatin (a chemotherapy agent) and Selenium can reduce serum levels of selenium.


  • The effects of Hyperthyroidism medication (Methimazole) can be reversed by taking Iodine, possibly causing hypothyroidism.
  • ACE inhibitors, (benazepril, fosinopril and lisinopril), used to treat high blood pressure can elevate potassium levels in the blood when taken with Iodine.
  • The risk of hyperkalaemia is increased when Iodine is taken with potassium sparing diuretics.


  • ACE inhibitors and ARBs (losartan), used to treat hypertension and heart disease, may reduce urinary Potassium excretion, which can lead to hyperkalaemia. 
  • The risk of hyperkalaemia is also increased when taking Potassium and potassium sparing diuretics.
  • Hypokalaemia (deficiency in Potassium) may occur, when being treated with loop diuretics (furosemide) as they increase urinary potassium excretion.


Any information or product suggested on this website is not intended to diagnose, treat, cure, or prevent any medical condition. Never disregard medical advice or delay in seeking it because of something you have read on this website. Consult your primary healthcare physician before using any supplements or making any changes to your regime.     


Related Articles 

Interactions between Vitamins & Minerals | HealthAid 



  1. Medication Interactions: Food, Supplements and Other Drugs | American Heart Association 
  2. Supplements and Drug Interactions - Consumer Reports 
  3. Drug Supplement Interactions - Dr Sarah Brewer 
  4. Dietary Supplement Fact Sheets ( 
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