Supplements that can be deadly when combined with prescription drugs

Daily supplements like calcium, vitamin K, and potassium can be deadly when combined with prescription drugs.

If you think you are not getting enough vitamin D, you can try supplements.


Vitamins are essential for maintaining optimal bodily 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 may suggest or prescribe supplements for severely deficient patients. The Centers for Disease Control and Prevention have found that Americans are particularly deficient in vitamin B6, iron,

Vitamin D

and vitamin C.

Although sales of supplements like vitamins have skyrocketed during the pandemic, taking these supplements in conjunction with certain prescription drugs can lead to dangerous health outcomes.

Robert Alesiani, PharmD, Director of Drug Therapy at Tabula Rasa Healthcare, spoke with Insider about daily vitamins that can become deadly when combined with certain prescription medications.

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

The association of St. John’s wort with HIV or post-transplant medications can be fatal.

Bottle of St. John's wort supplement sitting on a pharmacy shelf

Mario Tama/Getty Images

St. John’s wort is a commonly prescribed herbal remedy for


in Europe. Some controlled studies have shown that St. John’s wort improves symptoms of depression in patients with mild to moderate forms of the disease.

Alesiani said the herb can trigger the production of enzymes and proteins — found in the gut, liver and intestines — that speed up the rate at which drugs are absorbed by the body. Rapid absorption can reduce drug effectiveness because the body excretes drugs too quickly before it can be used.

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

Additionally, combining certain antidepressants with St. John’s wort may also increase the risk of serotonin toxicity, which can lead to diarrhea, fever, seizures, and sometimes death, according to the 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 binds to and can block the absorption of different


used to treat a variety of illnesses including


bladder infections and plague.

“If a patient is taking antibiotics for an infection, but they are taking it in combination with calcium supplements, it can block the absorption of those antibiotics and they may not be getting the adequate levels they need to manage this. infection,” Alesiani said.

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

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

Potassium supplements combined with heart medications can cause a dangerous increase in blood pressure.


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

Credit: Thu Thai Thanh / EyeEm/Getty Images

Potassium helps the body regulate heart rate, lower blood pressure, and support muscle and nerve function. Too much potassium can cause 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 raise blood levels to dangerous levels. These drugs include ACE inhibitors and angiotensin receptor blockers – which relax veins and arteries to lower blood pressure – aldosterone antagonists and other potassium-sparing diuretics, which treat high blood pressure by causing you to urinate on excess salt to make it easier for your heart to pump blood.

Vitamin K can reduce or improve the effectiveness of life-saving drugs that decrease blood clots.

vitamin k supplement pills and bottle

Anne Cusack/Los Angeles Times via Getty Images

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

heart disease

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

People who have had a heart attack or have formed a dangerous blood clot in the lungs or veins are prescribed warfarin, a blood thinner that prevents clotting. Plug

vitamin K

supplements containing warfarin will reduce or enhance the drug’s effectiveness, Alesiani said, increasing the risk of dangerous clotting or bleeding.

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

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