Dozens of people were under investigation for having orgies on drugs, police said Wednesday.

Nine people were arrested and 18 others booked without physical detention, the Seoul Metropolitan Police Agency said.

Twenty-one of them, including a married couple, met through ZleTalk, a chatting app, and gathered at motels in Seoul's Gangnam district to use methamphetamine, or meth, and engage in group sex.

They usually met in groups of four to eight at a time, police said.

Together, they are believed to have taken some 60 grams of methamphetamine, which is worth 200 million won ($185,000).

The drug went for 800,000 to 1.4 million won per gram except on a few occasions when it was given out for free.

It was not immediately clear how some of them obtained the drug, which is illegal in South Korea.

Nine people allegedly sold it by hiding it in coin-operated lockers in subway stations and later having the buyer retrieve it.

While some of the suspects had a history of drug abuse, many, including an aspiring model in her 20s, were first-timers, police said, adding they confiscated 50 grams of meth found in one suspect's car.

Two other suspects remained at large. They are allegedly the main drug dealers. (Yonhap)