Runny nose, sore throat, cough, fever, and difficulty breathing are all symptoms that could point to a viral infection. Unlike bacterial infections, they can't be treated with medications like antibiotics, but there are some herbs that can help with prevention—and potentially speed the healing process if a viral infection does occur.

Viruses "do their damage by invading human cells, taking over the machinery, and replicating themselves like mad," says Heather Moday, M.D., an allergist and immunologist who is board-certified in integrative and holistic medicine. There are no targeted medical treatments for viruses—antiviral medications may lessen the severity of symptoms, but they don't stop the virus directly.

Ultimately, the best defense against all infections is a healthy immune system (and other precautionary measures), and if you suspect you have a virus, it's always a good idea to check in with your doctor before trying any at-home remedies. Not all antivirals work the same with all conditions; for example, there is some evidence that elderberry might be harmful when treating the novel coronavirus, so check in with your health care provider if you have symptoms.

Many antiviral herbs have been studied, primarily in vitro, but it's important to know that human research is very limited, and more is needed before making definitive statements about the effects of natural antivirals.

Elderberry, or more technically, sambucus, is one of the most popular natural antivirals, and Aviva Romm, M.D., an integrative medicine doctor and a master herbalist, says it's her "go-to antiviral herb for early signs of the flu."

One study published in the Journal of Functional Food specifically looked at the influenza virus in vitro and found that elderberry extract1 "showed mild inhibitory effect at the early stages of the influenza virus cycle, with considerably stronger effect in the post-infection phase."

Supplementation with elderberry was also found to substantially reduce upper respiratory symptoms2 in a meta-analysis of research, which included 180 total participants, published in Complementary Theories in Medicine.

Romm recommends taking sambucas in tincture or syrup form—about 3 tablespoons a day for adults and 3 teaspoons per day for kids over 2 years old—at the earliest signs of symptoms. 

Curcumin, the main compound in turmeric, has been used in integrative medicine as far back as the 1700s.

In one study published in Antiviral Research, which specifically looked at Zika and chikungunya viruses in vitro, researchers found that the viruses "lost infectivity when incubated directly with curcumin3 or derivatives of curcumin, suggesting that curcumin alters the ability of the virus to infect cells." The researchers stated they believe curcumin reduces the viruses' ability to replicate, by keeping it from binding at the cell surface. 

Curcumin has also demonstrated antiviral activity against several different types of viruses4, according to a review of current research published in Frontiers in Microbiology.

Ellen Vora, M.D., who is board-certified in holistic and integrative medicine, says that you can take curcumin as a supplement (there's no one-size-fits-all dose, but a review of research published in Food noted that 500 to 2,000 milligrams5 has been used without any side effects) or cook with turmeric. She also recommends combining it with black pepper, which can increase its absorption rate.

Carvacrol is the primary active component in oregano oil, a potential natural antiviral that has been shown to break down viruses, reducing their ability to infect their host, according to the American Society for Microbiology.

Thymol, the other major component of oregano oil, may also possess antiviral qualities. In one in vitro study that was published in Planta Medica, thymol reduced the activity of the herpes virus7 by 90% within one hour.

Bindiya Gandhi, M.D., an American Board Family Medicine–certified physician, points out that oregano oil may also help fight inflammation—a hallmark of viral infections—and allergies. She recommends oregano oil capsules (taken as directed) over tinctures or drops since the oil can have a pungent flavor that can be off-putting. However, she says if you do take it in liquid form, put a few drops directly on your tongue every day.

Peppermint, or Mentha piperita, as it's officially known, is an herb that is said to have natural antiviral properties. In addition to menthol, which is found in the highest concentrations, it contains more than 40 compounds, like flavonoids, polyphenols, and tocopherols, that may play a role in keeping you healthy.

Peppermint oil, which is a concentrated form of the active compounds in peppermint, may be especially helpful. In one study that was published in Phytomedicine, researchers found that peppermint oil may reduce the viral activity of the herpes virus8, when exposed to it in a controlled lab setting.

Romm calls garlic, whose official name is Allium sativum L., "the original super-immunity herb." Garlic has been used as a therapeutic medicinal plant for centuries. Its main compound, called allicin, is said to have several health benefits, including antimicrobial activity.

Although there's been more research on garlic's effect on bacteria, a review published in the Avicenna Journal of Phytomedicine noted that studies have shown garlic extract may exhibit antiviral activity9 against several different types of viruses, like influenza and rhinovirus.

But the scant garlic you cook with likely isn't enough to fight off viral infections. You need concentrated doses, Moday says, "at the first sign of an infection, start eating one raw garlic clove daily, or use concentrated allicin extract."

Next to elderberry, echinacea may be one of the most well-known natural antivirals. However, even though it's a popular choice for immunity, it's important to note that studies have found mixed results on whether it's effective.

In one in vitro study published in Virology Journal, echinacea extract interfered with viral entry into cells. The research noted that the extract may reduce the activity of several different types of viruses, too. However, other studies haven't shown any positive effects.

There are several different types of echinacea, but the most widely used, and most commonly studied, is Echinacea purpurea, which is available as a tincture, spray, tablet, or tea.

Although the exact mechanisms of St. John's wort's natural antiviral activity aren't clear, researchers believe that the components in St. John's wort may alter proteins in the viruses10, preventing them from fusing with cell membranes and causing infection, according to Herbal Medicine.

Vora typically recommends taking 450 milligrams of St. John's wort twice a day for a month and then increasing to 900 milligrams twice per day. However, since the supplement is potent, she advises working closely with a practitioner to make sure you're using it safely.

Ginger, formally known as Zingiber officinale Roscoe, has many active compounds, including phenols, terpenes, and organic acids. However, the health benefits of ginger are largely connected to its phenolic compounds, specifically gingerols and shogaols. Over the years, research has shown that ginger may prevent the growth of viruses11 (as well as bacteria and fungi), according to a research review in Foods. 

In one in vitro study, researchers found fresh ginger stimulated mucosal cells to release IFN-β12, a type of cytokine that contributes to counteracting a viral infection. Another clinical trial that involved 60 volunteers with confirmed hepatitis indicated that ginger extract may decrease the activity of hepatitis C viruses13. 

Romm recommends choosing fresh or powdered organic ginger and adding it to smoothies or other recipes or steeping it as a tea. You can also get more concentrated doses of ginger in supplement form.

Scrophularia is a family of herbal plants commonly called figworts. There are nearly 200 species of Scrophularia, but one particular species, called Scrophularia scorodonia, may be especially helpful in fighting off viruses.

According to one research review, when Scrophularia scorodonia was exposed in vitro to HCoV-22E9, a type of human coronavirus infection, it revealed it may help prevent the virus from attaching14 to, and penetrating into, the cells of the body.

Scrophularia scorodonia is sold as an herbal supplement called Xuán Shēn, but you can get other forms of Scrophularia species under the name "figwort." While there's no standard dosage used in studies, the manufacturer recommends 300 milligrams per day.

The research and history around natural antivirals is intriguing, but there is still no proven evidence that these treatments are effective. While you may choose to try natural antivirals and antiviral herbs, all the usual general health recommendations apply when it comes to preventing viral infections.