Two of the widely used drugs in the fight against Covid-19 do not prevent death or reduce the time spent in hospital.
According to the World Health Organisation (WHO), only dexamethasone has shown effectiveness in treating severe Covid-19 cases.
Results from Solidarity Therapeutics Trial show the two drugs, remdesivir and interferon -- in a large study being conducted by WHO -- have little or no effect in reducing mortality or time in hospital.
Speaking during a media briefing, WHO Director-General Tedros Adhanom Ghebreyesus said: "For the moment, the corticosteroid dexamethasone is still the only therapeutic shown to be effective against Covid-19 for patients with severe disease."
Remdesivir, an antiviral drug, was originally developed to treat Ebola and hepatitis C.
Earlier in the year, it was approved for the treatment of Covid-19 after another study by the National Institutes of Health showed that it reduced recovery time and mortality rates in hospitalised patients.
But in the solidarity trial research that involved 11,266 adults from 405 hospitals in 30 countries, researchers found that neither Remdesivir, Hydroxychloroquine, Lopinavir, Interferon nor a combination of Interferon and Lopinavir definitely reduced mortality.
The conclusion was based on overall mortality, initiation of ventilation and duration of hospital stay.
While dexamethasone has shown effectiveness, it cannot be used early in Covid-19 patients because it can weaken a person's immune system, making it hard for a person to fight off the infection.
It works by suppressing the body's immune system, making sure that it does not overreact to the SARS-CoV-2, the virus that causes Covid-19 and cause a "cytokine storm".
When such a storm occurs, antibodies attack not only the virus, but healthy cells as well.