Nearly two-thirds of people using marijuana for medical reasons had decreased or stopped taking other medications early, results of a State Government survey show.

The survey, an Australian first, was conducted by the National Drug and Alcohol Research Centre.

Participants reported cannabis was useful in preventing side effects caused by conventional medicines.

The most common medical conditions the cannabis users suffered were arthritis, chronic pain, depression, nausea, muscle spasms and weight loss.

More than 70 per cent were concerned about marijuana's illegality and 54 per cent were scared of being arrested, but were willing to take the risk for the benefits of the drug.

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Tough new laws will come into force today to crack down on Cabramatta's drug and crime problems.

Premier Bob Carr said the $18.8 million Cabramatta Anti-Drug Strategy was a committed effort to return the area to people who lived and worked there.

"These new laws mean drug dealers will no longer be able to avoid prosecution by disposing of drugs before police can get at them," Mr Carr said.

The police will have the power to:

* Arrest anyone who enters or leaves a suspected drug house - unless they can establish a lawful purpose.

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