Samsung heir Lee Jae-yong has been convicted and fined for illegally using the sedative propofol.
The embattled businessman had taken the drug, commonly used as anaesthesia, dozens of times in recent years.
Under South Korean law, recipients of a controlled drug can be prosecuted as well as those who administer it.
The controversial heir had just been released on parole in August, having spent 20 months in jail for bribery and embezzlement convictions.
During his latest trial, prosecutors said that Lee used propofol multiple times between 2015 and 2020 under the guise of skin treatment.
But his lawyer claimed it was to treat psychological stress related to the hospitalisation of his father and his ongoing legal proceedings. Lee pleaded guilty to the charges.
On Tuesday a court fined him 70 million won ($59,000, £43,000). As propofol is less likely to be misused than many other controlled substances, offenders typically receive fines rather than jail terms.
While it is more commonly used to sedate patients undergoing surgery, propofol is also sometimes used recreationally. The singer Michael Jackson was found to have died from a propofol overdose in 2009.