Supplements That Can Be Deadly When Combined With Prescription Drugs

Everyday supplements like calcium, vitamin K, and potassium can turn deadly when combined with prescription medications.

Vitamin D supplements

If you don’t think you’re getting enough vitamin D, you may want to try supplements.


Vitamins are essential for maintaining optimal body functions, from regulating heartbeats to healing wounds.

In general, people can get most of the vitamins they need from eating a well-balanced diet, but doctors might suggest or prescribe supplements in severely deficient patients. The Centers for Disease Control and Prevention has found Americans are particularly deficient in vitamin B6, iron,

vitamin D

, and vitamin C.

Though sales for supplements like vitamins have skyrocketed during the pandemic, taking these supplements in conjunction with some prescription medications, can lead to dangerous health outcomes.

Robert Alesiani, PharmD, the chief pharmacotherapy officer at Tabula Rasa Healthcare, spoke with Insider about the everyday vitamins that can turn lethal when combined with certain prescription medications.

“It’s always good to have your doctor or a pharmacist know the supplements you’re taking in conjunction with your prescription medications,” Alesiani said.


Combining St. John’s wort with HIV or post-transplant medications could be fatal.

St. John's Wort supplement bottle sitting on pharmacy shelf

Mario Tama/Getty Images

St. John’s Wort is an herbal remedy routinely prescribed for


in Europe. Some controlled studies have found St. John’s Wort improves symptoms of depression in patients with mild to moderate forms of the illness.

Alesiani said the herb can trigger the production of enzymes and proteins — found in the gut, liver, and intestines — that expedite the speed in which drugs are absorbed by the body. The rapid absorption can reduce the efficacy of medicines, since the body excretes the drugs out too quickly before it can be used. 

Alesiani added St. John’s Wort can cause harm by reducing the efficacy of antiviral drugs called protease inhibitors, which block the replication of HIV cells in the body.

Furthermore, combining some antidepressants with St. John’s Wort can also increase the risk of serotonin toxicity, which can lead to diarrhea, fever, seizures, and sometimes death, according to Mayo Clinic.

Calcium, aluminum, and iron supplements carry a positive charge that blocks the absorption of antibiotics.

A staged photo showing pills spilling out of an orange bottle.

A staged photo showing pills spilling out of an orange bottle.

Darwin Brandis/Getty Images

Calcium, aluminum, and iron supplements all carry a positive charge (called a “cation”) that bind to and may block some absorption of different


used to treat a variety of diseases, including


, bladder infections, and the plague. 

“If a patient’s taking antibiotics for an infection, but they’re taking it in conjunction with calcium supplements, it can block the absorption of those antibiotics and they may not get the adequate levels that they need to manage that infection,” Alesiani said.

Antibiotics that become less effective when combined with these supplements include:

  • Ciprofloxacin, a medicine that belongs to the fluoroquinolones class of antibiotics. It is used to treat bacterial infections in many different parts of the body.
  • Ofloxacin, a medicine that belongs to the fluoroquinolones class of antibiotics. Ofloxacin can treat pneumonia, bladder infections, and prostate infections.
  • Demeclocycline, a medicine that belongs to the tetracyclines class of antibiotics. Demeclocycline can treat respiratory tract infections, skin and eye infections, and infections spread by ticks, lice, and mites.
  • Omadacycline, a medicine that belongs to the tetracyclines class of antibiotics. Omadacycline can be used to treat bacterial pneumonia, and acute bacterial skin and skin structure infections.


Potassium supplements combined with heart drugs can lead to a dangerous increase in blood pressure.


Bananas contain lots of potassium, which functions as an electrolyte and nutrient.

Credit: Thu Thai Thanh / EyeEm/Getty Images

Potassium helps the body regulate heartbeat, lower blood pressure, and aids in muscle and nerve functioning. Too much potassium can lead to harmful changes in heart rhythm and compromise kidney function, Insider previously reported.

Alesiani said potassium supplements used in conjunction with medications to treat heart problems or

high blood pressure

can cause blood levels to increase to dangerous levels. These medications include ACE inhibitors and angiotensin receptor blockers — which relax the veins and arteries to lower blood pressure —  aldosterone antagonists, and other potassium-sparing diuretics, which treat high blood pressure by making you pee out excess salt to make it easier for your heart to pump blood. 




Vitamin K can reduce or enhance the efficacy of life-saving medication that decreases blood clots.

vitamin k supplement pills and bottle

Anne Cusack/Los Angeles Times via Getty Images

Vitamin K, used for a variety of functions like maintaining bone strength and protecting against

heart disease

, is especially important in wound-healing. The vitamin turns blood from a liquid to a gel-like consistency that then forms a scab, stopping the body from bleeding to death. 

People who have had a heart attack or formed a dangerous blood clot in the lungs or veins are prescribed Warfarin, a blood-thinning medication that hinders clotting. Taking

vitamin K

supplements with Warfarin will either reduce or enhance the efficacy of this drug, Alesiani said, increasing the risk of dangerous clotting or bleeding.

“Because vitamins and other medications are available over the counter doesn’t necessarily mean that they’re considered safe in all cases,” Alesiani said.

By Percy