An anti-marijuana campaign in Australia featuring a human-sized lumbering stoned sloth acting foolishly has backfired and become the brunt of jokes on social media.

Launched this week using the slogan "You're worse on weed", it attempts to warn teenagers of the dangers of sustained cannabis use by depicting those who smoke it as grumbling, oversized "stoner sloths".

But it has been widely mocked as "ridiculously funny" with thousands of comments on its Facebook page, which has attracted more than 16,000 likes.

"Smoke weed, become one of the most adorable animals in the world. Where do I get some weed?" wrote Andrew Watton-Davies while Scott Hobson noted that: "I literally can't tell if it's satire or legit."

Even Premier Mike Baird, whose New South Wales state government is behind the campaign, has poked fun at it.

"Just saw the #StonerSloth ads. Not sure where NSW Gov's ad guys found Chewbaccas siblings, but those videos are ... Quite something," he tweeted, referring to the "Star Wars" character.

The National Cannabis Prevention and Information Centre said the ad did not reflect its views on how campaigns stressing the dangers of cannabis should be handled.

In a statement, it said any campaign should "be aware that teenagers are intelligent and have access to a lot of information, so campaign approaches should respect them and give them credit by avoiding hyperbole".

The NSW Greens called it "juvenile" but the state government insisted it was designed to reach young people before cannabis use became a serious problem.

"The campaign is designed to appeal to, and be 'shareable' among, teenagers who are some of the most vulnerable to cannabis use," it said.