An increasingly strange political scandal surrounding South Korean President Park Geun-hye has now left her office defending the purchase of hundreds of erectile dysfunction pills.

Park's office on Wednesday confirmed revelations by an opposition lawmaker that in December it purchased about 360 pills in total – 60 Viagra pills and the rest a generic version of the drug.

Park's office said the pills were bought to potentially treat altitude sickness for presidential aides and employees on Park's May trips to Ethiopia, Uganda and Kenya, whose capitals are up to two kilometres above sea level.

South Korean doctors sometimes prescribe Viagra-style drugs to climbers because they are believed to be effective in preventing altitude sickness.

"We bought them, but they were left unused," said Jung Youn-kuk, spokesman of the presidential Blue House.

Anti-aging purchases also cited

Viagra became the most searched keyword among South Koreans on the country's main online news portals following the news, which was initially reported by an opposition Democratic Party member of parliament.

Democratic MP Kim Sang-hee said data from the country's public health insurance review service showed Park's office also bought injections widely used in cosmetic and anti-aging treatments.

Park is now bracing for an impeachment push by opposition parties and some members of her own Saenuri Party amid allegations that she let a secretive confidante manipulate government affairs and amass an illicit fortune, a scandal critics say undermines the country's democracy.

On Sunday, prosecutors said they believe Park was collusively involved in the criminal activities of her longtime friend, Choi Soon-sil, and two presidential aides who allegedly bullied companies into giving tens of millions of dollars to foundations and businesses Choi controlled, and also enabled Choi to interfere with state affairs.