More than 1170 clubbers have pledged their support less than 24 hours after the Arches' announcement.
Regane MacColl, 17, died on Sunday, February 2 after spending Saturday night at The Arches and allegedly taking a "Mortal Kombat" ecstasy-type pill.
Now, hundreds of people have signed a petition calling for a change to the new policy to allow over 18s back to the venue.
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 ID's.
"The Arches is loved by many young people in Glasgow.
"People go to have a good night with friends, and enjoy music from DJs that come from all over the world.
"Now this is being jeopardised by one incident."
Police Scotland have issued a warning about the deadly red tablets following Ms MacColl's death.
Yesterday, the club said: "The Arches has been working closely with Police Scotland's licensing division to review our policies and do even more to ensure a safer clubbing environment within the venue.
"With immediate effect all club events will be open to over 21s only and valid ID will be required for entry."