POLITICIANS and anti-drug campaigners have labelled an annual festival in northern NSW promoting the use of cannabis as both dangerous and irresponsible.

Nimbin's MardiGrass and Cannabis Law Reform Weekend, which will be held for the 12th time on May 1-2, has grown into an international event attracting thousands of visitors.

But local federal National Party MP Ian Causley said the event was "totally irresponsible".

"This is a celebration of drugs and I don't approve of that," he said.

"Many of the arguments that are being put forward by this group for the legalisation of marijuana are being refuted in most of the medical reports."

Mr Causley said the police had a difficult job dealing with the drug culture in Nimbin which he described as a "sad place".

"You go out there and you see the drugs being pedalled," he said.

"I've been approached myself in the street and I'm the local member."

The MardiGrass features the Hemp Olympix with events such as joint rolling, bong throwing and growers' iron person Events.

Other events include book launches, film premieres, concerts, exhibitions, performances, the inaugural Marijuana Music Awards, pot poetry and pot art, the Cannabis Cup, Harvest Festival Ball and markets.

There will also be a protest march and a Rally for Cannabis Law Reform.

Queensland Drug and Alcohol Foundation chief executive Bob Aldred said it was irresponsible for the event to flaunt the law.

"We certainly wouldn't support the Hemp Mardigrass ... because this is an illegal drug," he said.

"Although it has many beneficial usages to use it from a black market source is just plain dangerous.

"I believe cannabis is certainly linked ... to mental illness particularly schizophrenia and other psychoses."

The Mardigrass will feature a Pot Psychosium which will tackle cannabis and mental health issues.

Organisers have invited doctors, health professionals, concerned parents and young cannabis users.

"Cannabis psychosis is the big stick used by prohibitionists these days and we hope to explore whether it's made of hardwood or hollow", Nimbin HEMP Embassy spokesman Michael Balderstone said.

"We hope to identify what is really going on from the experts in the field and gain some sort of consensus on what can be done to minimise harm, under the current constraints of prohibition."