A 33-year-old British citizen was found dead in a bathtub at Baan Yin Dee Hotel on Muen Ngern Road in Kathu district, Phuket, about 11.30pm on Monday.
The man was lying on his side and was believed to have drowned in the tub, police said on Tuesday. He wore only blue shorts.
Police found no traces of violence or robbery but there were liquor bottles on a TV shelf and two packs of Alprazolam, a medication used to treat anxiety and panic disorders. The packs were on the bed and one was empty.
An initial examination indicated the body had been in the bath about seven hours before being discovered. He was taken to Patong Hospital for a post mortem examination.
The man had checked in alone at the hotel on March 23 and was scheduled to check out today.
Hotel staff knocked his door about 11pm Monday as he had been inside for a long time and not been seen or heard from. A "do not disturb" sign was on the outside of the door.