''There are often two or three cases a week,'' a senior Phuket Tourist Police volunteer told Phuketwan this evening after an email alert was sent to all media.
While the release names one bar in Soi Paradise, the problem is widespread throughout Patong and occurs less frequently in other parts of Phuket.
''We see these guys carried out of one particular bar in Soi Bangla,'' the senior Tourist Police volunteer said. ''They are incoherent and usually vomiting badly.
''The police are aware of it - one of the bars where it happens is owned by a policeman.''
Robbery is usually the motive: ''If things are a little quiet, some of the hostesses will resort to drink-spiking to make ends meet.''
Frank Tomensen, Group Leader of the Phuket Tourist Police Foreign Volunteers in Patong, has instructed his patrol units to be on the lookout for victims who may appear impaired or disoriented.
''In two [recent] incidents that we are aware of, the victim had an odorless and colorless substance added to their drink while at a bar on Soi Paradise,'' he wrote in a message to officers and the Phuket media.
''The effects take about 15-20 minutes to set in, rendering the victim completely helpless. In both cases it is known the victims were robbed,'' Mr Tomenson said.
''The purpose of this alert is to let you know that this has been happening. In cases where you come across someone who is very impaired and disoriented [the drug loosens inhibitions and paralyzes motor control], they may not necessarily be drunk.
''This drug can have lethal effects, as it can slip a person into a coma-like state. Medical intervention is required as soon as possible.''
Visitors to Phuket are advised never to leave a drink unattended. The hotline for Tourist Police is 1155.