Updated

Thai police are cracking down on vendors in Bangkok's main backpacker district selling cheap doses of balloons filled with nitrous oxide, or laughing gas, to tourists.

Police say they noticed the trend a few weeks ago along Khao San Road, a pedestrian street lined with bars and cheap hotels, and have so far arrested eight vendors. Each dose sells for about 130 baht, or $4.

Bangkok police Lt. Col. Pitiphan Kridakorn said Monday that police are trying to curb sales of the drug-filled balloons before it gains wider popularity.

Illicit sales of nitrous oxide could cause harmful side effects to users and give the country a negative image, he said.

Those arrested face up to five years in prison and a $300 fine for selling medicine without authorization.