According to LIV Golf, McDowell's violation occurred in June at the league's Nashville event after the Northern Irishman took a decongestant medicine that included a banned substance called R-methamphetamine.
McDowell said in a statement on X that he was struggling with congestion that was affecting his sleep and used a "generic Vicks nasal decongestant" but didn't think to seek a therapeutic use exemption as he bought the medicine over the counter.
"As a professional golfer, I understand the importance of checking all medications and the option to apply for a Therapeutic Use Exemption," said McDowell. "Unfortunately, I did not think to do this ... and I deeply regret the oversight. I fully accept the sanctions imposed by LIV."
In accordance with LIV policy, both McDowell's and his Smash GC's team results from the Nashville event will be disqualified with prize money and points retroactively adjusted.
McDowell finished in a share of 42nd place at Nashville while Smash GC, a team captained by five-times major winner Brooks Koepka, finished 12th out of 13 teams.
McDowell, who won the 2010 US Open, will be eligible to return to competition at the September 13th-15th LIV Golf Chicago event and his vacancy on Smash GC will be filled by a to-be-confirmed reserve player at the August 16th-18th Greenbrier event.
