Up to a third of party drug users arrested in Guangdong are from Hong Kong, according to the head of the police Narcotics Bureau.
Cross-border excursions to rave parties - sometimes involving middle-aged people - had resulted in fewer party drugs being seized in Hong Kong, said Chief Superintendent Kenny Ip Lau-chuen.
'A recent example was when our counterpart at the Public Security Bureau raided a high-end, luxury disco in Shenzhen on November 29. Nine of the 40 people arrested for substance abuse were Hong Kong residents.
'Some of them were aged over 40,' Mr Ip said.
Party drugs were a third cheaper on the mainland than in Hong Kong, Mr Ip added.
The number of drug abuse cases was down in the first three-quarters of this year compared with the same period last year. The cases fell 16 per cent - from 13,529 to 11,333, police statistics showed.