Bosses at The Arches have decided to stop anyone under 21 from attending club nights following the suspected drugs death of a schoolgirl.
But Graeme Pearson, founder of the Scottish Drug Enforcement Agency (SCDEA), said club bosses were "shifting the problem elsewhere".
He believes targeting drug dealers would be more effective in preventing future deaths.
Hundreds of people have signed a petition opposing the club's new door policy.
Regane MacColl, 17, from Duntocher, Dunbartonshire, died in the early hours of Sunday, February 2 after becoming ill inside the club.
Police believe her death may be linked to 'mortal kombat' ecstasy tablets.
Mr Pearson, now a Labour MSP, said: "I understand why the club has done this, however, all they are doing is shifting the problem."
More than 1270 clubbers have already signed the anti-21 door policy petition.
The petition, called Get The Arches back to Over-18s, was posted online just hours after the club made the announcement.
It reads: "Changing the age restriction will in no way tackle this matter.
"It will only make promoters change venues and force people to get ID from somebody older or buy fake IDs.
"The Arches is loved by many young people in Glasgow.
"Now this is being jeopardised by one incident."
The unedr-21 ban starts immediately.