An Ethiopian pharmacy has been banned from trading for three months after a government inquiry confirmed it had illegally sold the blood-boosting drug EPO without a prescription, as revealed by a Guardian investigation.

The Gishen pharmacy in Addis Ababa, located metres away from the national stadium, sold nine vials of EPO to two different journalists within 26 minutes while the national athletics championships were taking place over the road. One pharmacist also admitted to having previously sold EPO to athletes.

An independent inquiry, ordered by the Ministry of Youth and Sports in Ethiopia following a joint investigation by the Guardian and the German broadcaster ARD, ruled that the branch of the pharmacy concerned should be temporarily closed.

The inquiry disproved the pharmacy manager’s claim that prescriptions had been sought before the EPO was dispensed to undercover journalists. It found no prescriptions were asked for, nor were any questions asked about why the medicine, a popular performance-enhancing drug for cyclists and athletes, was required.

Ethiopia is one of the dominant forces in distance running and the country’s athletes won five medals at this month’s world championships in London, including one for Muktar Edris, who beat Mo Farah to gold over 5,000m, and another for the world record holder Almaz Ayana, who won the women’s 10,000m. There is no suggestion of any wrongdoing by any of the medallists. But there have been sustained concerns over apparently lax anti-doping procedures in the country.

The Ethiopian Athletics Federation , of which Haile Gebreselassie is president, pledged to crack down on cheating in sport. Doping in the country has been criminalised, with prison time a possible punishment. But the Guardian and ARD filmed a top athlete admitting to having been on a doping programme before one of her most significant victories and looking for a new way to cheat the system.

A confused picture also emerged at the Ethiopian Anti-Doping Agency, which gave conflicting figures when asked to provide details of urine and blood tests during the national championships.