The MHRA has approved the antiviral Lagevrio (molnupiravir), one of two products health and social care secretary Sajid Javid said recently were in the pipeline.
The drug - which is the first approved antiviral for use against COVID-19 that can be taken orally in pill form - is effective at reducing risk of hospitalisation and death in people with mild to moderate infection with the virus who are at high risk of developing severe disease, the MHRA said.
Trials have found the drug works best when administered to patients in the early stages of infection, and the MHRA has recommended its use 'within five days of symptom onset'.
The regulator made clear that the treatment is 'not intended to be used as a substitute for vaccination against COVID-19' - and the government is yet to confirm how it will be rolled out for use in the NHS.
However, the drug has been authorised for use in people with mild to moderate COVID-19 and 'at least one risk factor for developing severe illness', such as obesity, age over 60 years, diabetes, or heart disease.
Mr Javid said: 'Today is a historic day for our country, as the UK is now the first country in the world to approve an antiviral that can be taken at home for COVID-19. This will be a gamechanger for the most vulnerable and the immunosuppressed, who will soon be able to receive the ground-breaking treatment.
'We are working at pace across the government and with the NHS to set out plans to deploy molnupiravir to patients through a national study as soon as possible.'
MHRA chief executive Dr June Raine said: 'Following a rigorous review of the data by our expert scientists and clinicians, we are satisfied that Lagevrio (molnupiravir) is safe and effective for those at risk of developing severe COVID-19 disease and have granted its approval.
'Lagevrio is another therapeutic to add to our armoury against COVID-19. It is also the world’s first approved antiviral for this disease that can be taken by mouth rather than administered intravenously. This is important, because it means it can be administered outside of a hospital setting, before COVID-19 has progressed to a severe stage.'