Can zinc, oregano oil, vitamin C or D prevent or treat COVID-19?

picture of a woman reading nutrition labels
The U.S. Centers for Disease Control and Prevention (CDC) has updated masking guidelines since this was written. Get the latest information.

There have been claims that COVID-19 can be prevented or cured by supplements like vitamin C, vitamin D, zinc or oregano essential oil. Here, infectious diseases expert Susan Swindells, MBBS, gives an update on scientific studies. Dr. Swindells was chosen by Anthony Fauci, MD, to be a member of the NHS COVID-19 Guidelines panel.

Vitamin C

"There are some studies looking at vitamin C and patients with COVID-19, but we don't have any results from them yet," says Dr. Swindells.

Taking high doses of vitamin C can cause nausea and diarrhea, especially if you exceed the daily recommended doses.

See the latest NIH guidelines on Vitamin C and COVID-19

Vitamin D

For vitamin D and COVID-19, several studies are ongoing and some have already been completed. Dr. Swindells says, "Vitamin D is a benign drug, and a lot of people take it, but there's no clear evidence of benefit for prevention or treatment of COVID-19."

Too much vitamin D can result in high levels of calcium in the blood, which can cause nausea, vomiting and kidney stones.

See the latest NIH guidelines on vitamin D and COVID-19


In a test tube, zinc interacts in a way that's helpful for curing viruses. Studies are looking at if the same thing happens in humans as well. But there's been no obvious benefit from any of the studies done so far. 

"Too much zinc causes neurologic problems like nerve damage," says Dr. Swindells. The recommended dietary allowance of zinc for adult women is 8 mg, and 11 mg for adult men.

See the latest NIH guidelines on zinc and COVID-19

Essential oils, like oregano

Currently, there are no studies testing if oregano essential oil can prevent or treat COVID-19. "There have been no essential oil studies with COVID-19 at all," says Dr. Swindells.

See what pharmacist Ally Dering-Anderson, PharmD, says about the safety and usefulness of essential oils.

The bottom line is that none of these supplements have shown efficacy against COVID-19 yet. So if you'd like to take supplemental vitamins, check with your primary care provider first. "If you take too much of anything, there's risk," says Dr. Swindells. "Don't take supplements that exceed the recommended dietary allowance." 

Dr. Swindells expects that more of these studies will be completed in the coming months. In the meantime, there are things you can do to protect yourself. "Wear a mask, stay away from people when you can, wash your hands and get a vaccine when someone offers it to you," she advises.