A Liberal backbencher has again hit out at his own State Government over the availability of synthetic drugs in Western Australia.

After raising concerns last week that synthetic cannabis was readily available in his southern suburbs electorate, Phil Edman has now legally bought what he believes is another questionable substance.

He said the breath spray bought at a Rockingham shopping centre was described on the packet as "liquid marijuana", and was being marketed to minors.

It was being sold as "a way to get high in class".

A manufacturer's warning said the product did not contain any marijuana, but Mr Edman believed it was made up of dangerous chemicals.

"I mean really what is going on, the Premier needs to intervene, we need urgent action," he said.

Mr Edman said included in the product's ingredients was a chemical called T-Maz20, which he researched and found that if it was inhaled or swallowed, users were advised to seek immediate medical attention.

He said although the manufacturer states that the product contains no real marijuana or any mind-altering substance, it was being marketed at impressionable youth.

Mr Edman emailed all Liberal MPs and staffers yesterday drawing attention to the "liquid marijuana" he had bought.

Police Minister Liza Harvey responded by sending out a warning via reply all email which said:

"You may have just broken the law and somewhat unwisely told a heap of people about it. I advise that you turn your contraband purchase into police immediately and seek legal advice. Please be assured that I am working on a solution to this issue that will provide you and our team with a win in our communities."

Edman willing to be arrested over 'cannabinoid plague'

The liquid "cannabis" and "weed" on sale at a Rockingham shop.

Mr Edman said he is willing to be arrested if that is what it takes to draw attention to the synthetic cannabinoid plague in his Rockingham electorate.

"These products are priming impressionable young children with the idea it’s fun to be high," he said.

And he is unconvinced much is changing.

"Nothing has changed in two weeks since I raised this issue," he said.

"If these [synthetic cannabinoid] products are illegal, then how come you can still buy them right across the road from a high school?"

Mr Edman previously accused his Cabinet colleagues of not doing enough to stamp it out, and took a sample of synthetic cannabis into Parliament to prove it was readily available.

His office had purchased a range of synthetic cannabis products from two local stores in his electorate, including one called Climax, which cost $70 and was the strongest of the substances available.

Mr Edman said one of the shops was across from one of the high schools in his electorate.

Premier Colin Barnett said the Government was committed to new laws which would ban any psycho-active substance, unless it was approved for medical purposes.

But he said it was not the easiest legislation to draft.

Mr Barnett also criticised Mr Edman for bringing Climax into the Parliament.

"Work is being undertaken now to have a more general prohibition on these substances," Mr Barnett said.

"I don’t think he needs to bring substances into the Parliament."