The Covid-19 pandemic is one of the greatest challenges modern medicine has ever faced. Doctors and scientists are scrambling to find treatments and drugs that can save the lives of infected people and perhaps even prevent infection.

Below is an updated list of 19 of the most-talked-about treatments for the coronavirus. While some are accumulating evidence that they’re effective, most are still at early stages of research. We also included a warning about a few that are just bunk.

There is no cure yet for Covid-19. And even the most promising treatments to date only help certain groups of patients, and await validation from further trials. The F.D.A. has not fully licensed any treatment specifically for the coronavirus, but it has granted emergency use authorization to a few.

We will update and expand the list as new evidence emerges. For details on evaluating treatments, see the N.I.H. Covid-19 Treatment Guidelines. For the current status of vaccine development, see our Coronavirus Vaccine Tracker.

What the Labels Mean

WIDELY USED: These treatments have been used widely by doctors and nurses to treat patients hospitalized for diseases that affect the respiratory system, including Covid-19.

PROMISING EVIDENCE: Early evidence from studies on patients suggests effectiveness, but more research is needed. This category includes treatments that have shown improvements in morbidity, mortality and recovery in at least one randomized controlled trial, in which some people get a treatment and others get a placebo.

TENTATIVE OR MIXED EVIDENCE: Some treatments show promising results in cells or animals, which need to be confirmed in people. Others have yielded encouraging results in retrospective studies in humans, which look at existing datasets rather than starting a new trial. Some treatments have produced different results in different experiments, raising the need for larger, more rigorously designed studies to clear up the confusion.

NOT PROMISING: Early evidence suggests that these treatments do not work.

PSEUDOSCIENCE OR FRAUD: These are not treatments that researchers have ever considered using for Covid-19. Experts have warned against trying them, because they do not help against the disease and can instead be dangerous. Some people have even been arrested for their false promises of a Covid-19 cure.

Blocking the Virus

Antivirals can stop viruses such as H.I.V. and hepatitis C from hijacking our cells. Scientists are searching for antivirals that work against the new coronavirus.

PROMISING EVIDENCE
EMERGENCY USE AUTHORIZATION

Remdesivir
Remdesivir, made by Gilead Sciences, was the first drug to get emergency authorization from the F.D.A. for use on Covid-19. It stops viruses from replicating by inserting itself into new viral genes. Remdesivir was originally tested as an antiviral against Ebola and Hepatitis C, only to deliver lackluster results. But preliminary data from trials that began this spring suggested the drug can reduce the recovery time of people hospitalized with Covid-19 from 15 to 11 days. (The study defined recovery as “either discharge from the hospital or hospitalization for infection-control purposes only.”) These early results did not show any effect on mortality, though retrospective data released in July hints that the drug might reduce death rates among those who are very ill.

TENTATIVE OR MIXED EVIDENCE

Favipiravir
Originally designed to beat back influenza, favipiravir blocks a virus’s ability to copy its genetic material. A small study in March indicated the drug might help purge the coronavirus from the airway, but results from larger, well-designed clinical trials are still pending.

TENTATIVE OR MIXED EVIDENCE

EIDD-2801
Another antiviral originally designed to fight the flu, EIDD-2801 has had promising results against the new coronavirus in studies in cells and on animals. It is still being tested in humans.

TENTATIVE OR MIXED EVIDENCE

Recombinant ACE-2
To enter cells, the coronavirus must first unlock them — a feat it accomplishes by latching onto a human protein called ACE-2. Scientists have created artificial ACE-2 proteins which might be able to act as decoys, luring the coronavirus away from vulnerable cells. Recombinant ACE-2 proteins have shown promising results in experiments on cells, but not yet in animals or people.

NOT PROMISING

Lopinavir and ritonavir
Twenty years ago, the F.D.A. approved this combination of drugs to treat H.I.V. Recently, researchers tried them out on the new coronavirus and found that they stopped the virus from replicating. But clinical trials in patients proved disappointing. In early July, the World Health Organization suspended trials on patients hospitalized for Covid-19. But they didn’t rule out studies to see if the drugs could help patients not sick enough to be hospitalized, or to prevent people exposed to the new coronavirus from falling ill. The drug could also still have a role to play in certain combination treatments.

NOT PROMISING

Hydroxychloroquine and chloroquine
German chemists synthesized chloroquine in the 1930s as a drug against malaria. A less toxic version, called hydroxychloroquine, was invented in 1946, and later was approved for other diseases such as lupus and rheumatoid arthritis. At the start of the Covid-19 pandemic, researchers discovered that both drugs could stop the coronavirus from replicating in cells. Since then, they’ve had a tumultuous ride. A few small studies on patients offered some hope that hydroxychloroquine could treat Covid-19. The World Health Organization launched a randomized clinical trial in March to see if it was indeed safe and effective for Covid-19, as did Novartis and a number of universities.

Meanwhile, President Trump repeatedly promoted hydroxychloroquine at press conferences, touting it as a “game changer,” and even took it himself. The F.D.A. temporarily granted hydroxychloroquine emergency authorization for use in Covid-19 patients — which a whistleblower later claimed was the result of political pressure. In the wake of the drug’s newfound publicity, demand spiked, resulting in shortages for people who rely on hydroxychloroquine as a treatment for other diseases.

When data emerged from the randomized clinical trials, the message was clear: hydroxychloroquine didn’t help people with Covid-19 get better or prevent healthy people from contracting the coronavirus. Another randomized clinical trial found that giving hydroxychloroquine to people right after being diagnosed with Covid-19 didn’t reduce the severity of their disease. (One large-scale study that concluded the drug was harmful as well was later retracted.) The World Health Organization, the National Institutes of Health and Novartis have since halted trials investigating hydroxychloroquine as a treatment for Covid-19, and the F.D.A. revoked its emergency approval. The F.D.A. now warns that the drug can cause a host of serious side effects to the heart and other organs when used to treat Covid-19.

In July, researchers at Henry Ford hospital in Detroit published a study finding that hydroxychloroquine reduced mortality in Covid-19 patients. President Trump praised the study on Twitter, but experts raised doubts about it because it was not a randomized controlled trial. Still, the White House has initiated a push for the F.D.A. to reauthorize hydroxychloroquine as an emergency Covid-19 treatment.

Despite negative results, a number of hydroxychloroquine trials have continued. A recent analysis by STAT and Applied XL found more than 180 ongoing clinical trials testing hydroxychloroquine or chloroquine, for treating or preventing Covid-19. Although it’s clear the drugs are no panacea, it’s possible they could work in combination with other treatments, or when given in early stages of the disease.

Mimicking the Immune System

Most people who get Covid-19 successfully fight off the virus with a strong immune response. Drugs might help people who can’t mount an adequate defense.

TENTATIVE OR MIXED EVIDENCE

Convalescent plasma
A century ago, doctors filtered plasma from the blood of recovered flu patients. So-called convalescent plasma, rich with antibodies, helped people sick with flu fight their illness. Now researchers are trying out this strategy on Covid-19. Early trials with convalescent plasma have yielded promising, if preliminary, results, and the F.D.A. has authorized its use on very sick patients infected by the coronavirus.

TENTATIVE OR MIXED EVIDENCE

Monoclonal antibodies
Convalescent plasma contains a mix of different antibodies, some of which can attack the coronavirus, and some of which can’t. Researchers have been sifting through the slurry for the most potent antibodies against Covid-19. Synthetic copies of these molecules, known as monoclonal antibodies, can be manufactured in bulk and then injected into patients. Safety trials for this treatment have only just begun, with several more on the way.

TENTATIVE OR MIXED EVIDENCE

Interferons
Interferons are molecules our cells naturally produce in response to viruses, rousing the immune system to attack. Injecting synthetic interferons is now a standard treatment for a number of immune disorders. Rebif, for example, is prescribed for multiple sclerosis. Early studies, including experiments in mice and cells, hint that injecting interferons may help against Covid-19. There’s even some evidence that the molecules could help prevent healthy people from getting infected.

Putting Out Friendly Fire

The most severe symptoms of Covid-19 are the result of the immune system’s overreaction to the virus. Scientists are testing drugs that can rein in its attack.

PROMISING EVIDENCE

Dexamethasone
This cheap and widely available steroid blunts many types of immune responses. Doctors have long used it to treat allergies, asthma and inflammation. In June, it became the first drug shown to reduce Covid-19 deaths. That study of more than 6,000 people, which in July was published in the New England Journal of Medicine, found that dexamethasone reduced deaths by one-third in patients on ventilators, and by one-fifth in patients on oxygen. It may be less likely to help — and may even harm — patients who are at an earlier stage of Covid-19 infections, however. In its Covid-19 treatment guidelines, the National Institutes of Health recommends only using dexamethasone in patients with COVID-19 who are on a ventilator or are receiving supplemental oxygen.

TENTATIVE OR MIXED EVIDENCE

Cytokine Inhibitors
The body produces signaling molecules called cytokines to fight off diseases. But manufactured in excess, cytokines can trigger the immune system to wildly overreact to infections, in a process sometimes called a cytokine storm. Researchers have created a number of drugs to halt cytokine storms, and they have proven effective against arthritis and other inflammatory disorders. Some turn off the supply of molecules that launch the production of the cytokines themselves. Others block the receptors on immune cells to which cytokines would normally bind. A few block the cellular messages they send.

Against the coronavirus, several of these drugs, including tocilizumab, sarilumab and anakinra, have offered modest help in some trials, but faltered in others. The drug company Regeneron recently announced that a branded version of sarilumab, Kevzara, failed Phase 3 clinical trials.

TENTATIVE OR MIXED EVIDENCE
EMERGENCY USE AUTHORIZATION

Cytosorb
Cytosorb is a cartridge that filters cytokines from the blood in an attempt to cool cytokine storms. The machine can purify a patient’s entire blood supply about 70 times in a 24-hour period. It was granted emergency use authorization by the F.D.A. for Covid-19 based on a small study in March suggesting that it had helped dozens of severely ill Covid-19 patients in Europe and China. Further trials on patients with Covid-19 are now underway.

TENTATIVE OR MIXED EVIDENCE

Stem cells
Certain kinds of stem cells can secrete anti-inflammatory molecules. Over the years, researchers have tried to use them as a treatment for cytokine storms, and now dozens of clinical trials are under way to see if they can help patients with Covid-19. But these stem cell treatments haven’t worked well in the past, and it’s not clear yet if they’ll work against the coronavirus.

Other Treatments

Doctors and nurses often administer other supportive treatments to help patients with Covid-19.

WIDELY USED

Prone positioning
The simple act of flipping Covid-19 patients onto their bellies opens up the lungs. The maneuver has become commonplace in hospitals around the world since the start of the pandemic. It might help some individuals avoid the need for ventilators entirely. The treatment’s benefits continue to be tested in a range of clinical trials.

WIDELY USED
EMERGENCY USE AUTHORIZATION

Ventilators and other respiratory support devices
Devices that help people breathe are an essential tool in the fight against deadly respiratory illnesses. Some patients do well if they get an extra supply of oxygen through the nose or via a mask connected to an oxygen machine. Patients in severe respiratory distress may need to have a ventilator breathe for them until their lungs heal. Doctors are divided about how long to treat patients with noninvasive oxygen before deciding whether or not they need a ventilator. Not all Covid-19 patients who go on ventilators survive, but the devices are thought to be lifesaving in many cases.

TENTATIVE OR MIXED EVIDENCE

Anticoagulants
The coronavirus can invade cells in the lining of blood vessels, leading to tiny clots that can cause strokes and other serious harm. Anticoagulants are commonly used for other conditions, such as heart disease, to slow the formation of clots, and doctors sometimes use them on patients with Covid-19 who have clots. Many clinical trials teasing out this relationship are now underway. Some of these trials are looking at whether giving anticoagulants before any sign of clotting is beneficial.

Pseudoscience and Fraud

False claims about Covid-19 cures abound. The F.D.A. maintains a list of more than 80 fraudulent Covid-19 products, and the W.H.O. debunks many myths about the disease.

WARNING: DO NOT DO THIS

Drinking or injecting bleach and disinfectants
In April, President Trump suggested that disinfectants such as alcohol or bleach might be effective against the coronavirus if directly injected into the body. His comments were immediately refuted by health professionals and researchers around the world — as well as the makers of Lysol and Clorox. Ingesting disinfectant would not only be ineffective against the virus, but also hazardous — possibly even deadly. In July, Federal prosecutors charged four Florida men with marketing bleach as a cure for COVID-19.

WARNING: NO EVIDENCE

UV light
President Trump also speculated about hitting the body with “ultraviolet or just very powerful light.” Researchers have used UV light to sterilize surfaces, including killing viruses, in carefully managed laboratories. But UV light would not be able to purge the virus from within a sick persons’ body. This kind of radiation can also damage the skin. Most skin cancers are a result of exposure to the UV rays naturally present in sunlight.

WARNING: NO EVIDENCE

Silver
The F.D.A. has threatened legal action against a host of people claiming silver-based products are safe and effective against Covid-19 — including televangelist Jim Bakker and InfoWars host Alex Jones. Several metals do have natural antimicrobial properties. But products made from them have not been shown to prevent or treat the coronavirus.

Tracking the Coronavirus

Note: After additional discussions with experts we have adjusted several labels on the tracker. The “Strong evidence” label has been removed until further research identifies treatments that consistently benefit groups of patients infected by the coronavirus. In its place, “Promising evidence” will be used for drugs such as remdesivir and dexamethasone that have shown promise in at least one randomized controlled trial, and “Widely used” for treatments such as proning and ventilators that are often used with severely ill patients, including those with Covid-19. And we may reintroduce the “Ineffective” label when ongoing clinical trials repeatedly end with disappointing results.

Sources: National Library of Medicine; National Institutes of Health; Paul Knoepfler, University of California, Davis; Phyllis Tien, University of California, San Francisco; John Moore and Douglas Nixon, Weill Cornell Medical College; Noah Haber, Stanford University.