Since January, hundreds of scientific teams and biotech companies have been developing and testing treatments for COVID-19.

Already, clinical trials have found several drugs that appear to help, lowering the risk of death, shortening hospital stays, or reducing the severity of the disease. But other once-promising COVID-19 treatments have fallen flat when tested on patients in controlled studies.

Here's our latest, evidence-based coronavirus treatment update, including the options that appear to work, those that don't, and the ones researchers still aren't sure about.

Stuff that (Probably) Works

Dexamethasone

In June, researchers involved in the United Kingdom's huge RECOVERY trial reported that dexamethasone (a cheap, readily available steroid) reduced death rates in ventilated patients by nearly one-third, from 40% to 28% — making it the first proven, life-saving coronavirus treatment.

The steroid had no benefit for patients with milder cases of COVID-19, but the researchers advised using dexamethasone to treat more severe cases.

The drug probably works by tamping down the immune system's overreaction (called a cytokine storm), which kills many patients with severe COVID-19. But for patients with less advanced cases, there would be no benefit (and possibly some harm) from reducing their immune response, so the steroid should be used as a last resort.

A month later, the researchers published their peer-reviewed study on dexamethasone in the New England Journal of Medicine, which confirmed their early data. On September 2, a meta-analysis of clinical studies undertaken by the WHO and published in JAMA found an association between dexamethasone and lower mortality rates in patients with severe cases of COVID-19.

Remdesivir

Researchers began testing the antiviral drug remdesivir on COVID-19 patients in February, encouraged by the drug's efficacy against other coronaviruses in animal testing.

In April, several groups reported that patients given the drug showed signs of improvement and quicker recovery times, reducing time to recovery by about a third. On May 1, the FDA issued the drug's maker — Gilead Sciences — an emergency use authorization for remdesivir as a potential coronavirus treatment.

Unlike dexamethasone, other studies have found no benefit of remdesivir for advanced cases of COVID-19. Because antiviral drugs work by slowing down the replication of the virus, they are more effective when given early on, before the body is overwhelmed with viruses.

Several clinical trials of the drug are ongoing — including a pediatric trial and one that tests whether it's more effective when paired with tocilizumab, an anti-inflammatory drug — but already, remdesivir is one of the most promising COVID-19 treatments available.

Too Soon to Say

Convalescent Plasma Therapy

On August 23, the FDA issued a controversial emergency use authorization for transfusions of blood plasma from coronavirus survivors — also known as convalescent plasma therapy — as a COVID-19 treatment, noting that 70,000 American patients had already received it.

The path to this began in April, when two studies in China found that patients with severe cases of COVID-19 benefited from convalescent plasma therapy. The theory behind the treatment is that survivors' blood plasma has antibodies, which can help neutralize the virus in patients with active infections.

Since then, the preliminary results from studies have been mostly positive.

One study involving more than 35,000 patients reported that giving patients convalescent plasma within three days of diagnosis produced a statistically significant decrease in mortality compared to those given it four or more days after. However, that study has yet to be peer reviewed.

Famotidine

One of the most unlikely potential COVID-19 treatments has been famotidine, the active ingredient in the over-the-counter heartburn drug Pepcid.

Early in the pandemic, reports began circulating in China that patients who took famotidine had better outcomes. Despite only anecdotal evidence, several groups launched clinical trials to test the drug.

So far, it seems famotidine doesn't directly target the coronavirus, but it does appear to be connected to better patient outcomes. More research is needed, though, before famotidine can be confirmed as an effective coronavirus treatment.

Favipiravir

Developed by Fujifilm Toyama Chemical in 2014 as a flu treatment, favipiravir has gotten new life as a promising coronavirus treatment.

In March, Chinese officials reported that the drug was "clearly effective" in two clinical trials involving 320 COVID-19 patients — in one of the trials, it cut the average recovery time from 11 days to just four.

Several nations, including Russia, China, and India, have since approved the drug's use as a COVID-19 treatment. It has yet to receive approval in the U.S., though, but as recently as July 6, new trials were still getting underway stateside.

LY-CoV555

Canadian biotech firm AbCellera and U.S.-based pharmaceutical company Eli Lilly have used a blood sample from a single coronavirus survivor to develop LY-CoV555, a drug that contains a coronavirus antibody that, in animal models, prevented the virus from infecting cells.

On June 1, Eli Lilly kicked off its first human trial of LY-CoV555, giving it to 32 hospitalized COVID-19 patients in the U.S. That trial is expected to take two months, and if the results are positive, the pharma company hopes to launch large efficacy trials soon after.

In August, the NIH announced plans to test LY-CoV555 in a Phase 2 and 3 trial (ACTIV-2), and Eli Lilly launched a Phase 3 trial to test the drug's ability to prevent coronavirus infections.

If LY-CoV555 proves effective as a coronavirus treatment or prophylactic, Eli Lilly expects it could manufacture several hundred thousand doses before the end of 2020.

See More: Public Health First Coronavirus Antibody Drug Trial Launches in US

Tocilizumab

As recently as mid-July, the rheumatoid arthritis medication tocilizumab (brand name Actemra) was looking like one of the more promising COVID-19 treatments — a retrospective study found that it appeared to decrease ventilated patients' risk of death from COVID-19 by 45%.

But just two weeks later, drugmaker Roche announced the disappointing results of a late-stage clinical trial of tocilizumab, reporting that it failed to beat a placebo at improving hospitalized patients' clinical status or reducing their chances of dying.

Tocilizumab did, however, appear to reduce the amount of time COVID-19 patients spent in the hospital — from an average of 28 days down to 20 — and other trials of the arthritis drug are ongoing, so there is a chance it could still emerge as a useful coronavirus treatment.

Interferons

Interferons are immune proteins that help fight infections by interfering with a virus’s ability to replicate. Studies have show that they could be useful as a COVID-19 treatment — but the timing of the delivery is key.

Given soon after a patient contracts COVID-19, and they appear capable of providing an immune boost that can speed up recovery.

But because one of the hallmarks of COVID-19 is its ability to cause a harmful overreaction of the immune system — a cytokine storm — a late delivery of interferons could make an illness worse.

Several studies of interferons are still ongoing — including one testing its ability to boost the benefits of remdesivir — so we’ll likely learn more about their utility as a COVID-19 treatment in the near future.

Very Doubtful

Chloroquine / Hydroxychloroquine

In lab studies, the malaria drug chloroquine showed promise in preventing and treating SARS infections, making it a solid candidate as a novel coronavirus treatment.

In March, the FDA granted chloroquine and its alternative formulation, hydroxychloroquine, emergency use authorizations, clearing doctors to prescribe both as COVID-19 treatments, often combined with zinc or the antibiotic azithromycin.

However, the drugs failed to live up to their promise during rigorous clinical testing, and the FDA revoked the authorizations on June 18.

Multiple studies around chloroquine have been corrected, withdrawn, criticized, or retracted, including two papers in the Lancet and NEJM that claimed the drug increased the risk of dying for COVID-19 patients.

Lopinavir and Ritonavir

In January, China began recommending that doctors treat COVID-19 patients with the HIV drugs lopinavir and ritonavir. By March, several research groups were testing the drug combination's efficacy in clinical trials.

Early reports from those trials were disappointing, though, and the ones that trickled in over the next few months were no better. In July, the WHO announced it was officially discontinuing the lopinavir/ritonavir arm of its massive SOLIDARITY trial.

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