Police are frustrated by their inability to take blood tests from people they suspect of driving under the influence of party pills.

Constable Sean Drader said young people thought it was legal to drive after taking the pills.

"But if you're driving so poorly that you are all over the road, then it is illegal," he said.

"No one has done any tests to say what the legal limit should be."

Mr Drader's comments follow the arrest of a 17-year-old youth driving in Queenstown on Friday after being suspected of swallowing 40 party pills.

A medical examination was ordered but a blood test could not be done because no alcohol was involved, Mr Drader told the Southland Times.

The youth is due to appear in court tomorrow on four charges, including careless driving, possession of a cannabis pipe and driving while disqualified.

Mr Drader said the party pill culture was huge and that it was up to the public to lobby the Government on policing it.

"It's not up to the police to influence government. The public has to go to their local member and do something about it," he told the newspaper.

A Lakes District Hospital spokesman told the newspaper the hospital treated two to three cases a week involving party pills.