WorkSafe is cracking down on the volume of alcohol and drugs being used by builders in the Christchurch rebuild.

A recent study found that 18 percent of construction workers say there are people working hungover or stoned “from time to time, to a lot” on site.

Project Manager Donna Burt said it's a significant issue for the construction sector that's often treated too lightly.

"They think if they've had a bit of a sleep and are back at work and should be okay, what we see out there is people who are hungover or have been taking drugs are not as sharp as they should be, and much more likely to have an accident."

Donna Burt is addressing both employers and workers on how they can manage alcohol and drug use on site at a trade breakfast this morning.

She believes it's time employers wake up to the problem.

"What we're trying to do is get them to think about how they can actually prevent it being an issue, and then how they can manage it."

"What we've done is put some information together for them about developing drug and alcohol policies."