Seven workers were banned from the central city rebuild in March after returning positive drug tests.
The seven are among 16 workers who have had their accreditation cancelled by the Canterbury Earthquake Recovery Authority over drugs since the demolitions and rebuilds began.
CERA has a zero tolerance police for drugs and alcohol, but leaves it up to individual contracting companies to conduct pre-employment and random testing.
Latest figures provided to The Star show that four workers were banned in March 2012, four more in June and one in August, before the seven last March.
The type of drugs involved was unavailable.
"Individual companies aren't asked to provide that level of personal detail as it's none of CERA's business what the substance was," a CERA spokeswoman said.
"They just indicate that a person has breached their drug and alcohol policy and we've then cancelled their passes."
CERA chief executive Roger Sutton has credited the health and safety protocols used by demolition and building companies for keeping staff safe over the last two years.
"Over the life of the CBD cordon we have had one serious accident and no workplace deaths," Mr Sutton said. "That's absolutely outstanding given the huge amount of dangerous work that has been going on."
He said CERA would continue to support companies who dismiss their staff over breaches of drug and alcohol policy.
Nikau Contractors Ltd national health and safety manager Helina Stil said the company had 40 staff working in the central city zone and none had tested positive for drugs or alcohol.
Ms Stil said she'd heard of some workers being banned "but I didn't realise there had been that many".
Nikau conducted pre-employment, post-incident and random testing.
"The last thing you need in a very dangerous industry is someone stoned or having had alcohol working alongside you," she said.
A spokesman for Fletcher Construction said the company had zero tolerance for drugs in the workplace. Prescription drugs were not included if they were prescribed for the person.
"We believe our policy and processes are consistent with those of other major companies operating in the construction sector," he said.
"All Fletcher employees are required to have a pre-employment drug and alcohol test. Random, just cause and post-incident or accident testing are also carried out on our sites."