The Food and Drug Administration (FDA) is warning people against using the antiparasitic drug Ivermectin to treat Covid-19, saying it is mostly for use in animals.
"Ivermectin is technically not produced to be used on people so the risks are greater than drugs specifically developed for humans.
"People must not buy it without a prescription and in any case, a study on its effectiveness against the virus has yet to be concluded," FDA deputy secretary-general Surachoke Tangwiwat said on Tuesday.
Mr Surachoke said although Ivermectin is mainly used on animals, it has been used in isolated cases to treat specific types of parasite and scabies in humans.
The drug has been trialed for battling Covid-19. However, while some studies suggested it is effective against the virus others found it ineffective.
There is nothing conclusive about the drug's efficacy in fighting Covid-19, he said.
Ivermectin can cause several adverse side effects, such as a rash, urticaria, queasiness, dizziness and also may have a harmful effect on the nervous and system and people's sight.
Recent messages that went viral in social media claimed a sharp drop in Covid-19 cases in some Indian cities was attributed to the use of Ivermectin.
It also claimed that Ivermectin was favoured among people in poor countries as it is cheap and easy to buy.
However, the drug has not been declared safe for use to treat Covid-19 by the World Health Organization.
Chiang Mai University's Faculty of Pharmacy called the Covid cure claims fake news that could have "terrifying consequences" as it prompted mostly elderly people to buy the drug who mistakenly thought it could protect them.
The university's website said that the drug may aggravate Covid-19 patients' symptoms, according to the website.
The reported drop in Covid-19 cases in India was the result of more vaccines being made available to the population, the website said.