A Perth after-hours medical clinic says the number of patients using its service has reduced by almost a third since a government crackdown but concedes the system was being abused, including by doctors writing opioid scripts.

The Federal Government crackdown on false claims for urgent after hours care only began on March 1.

But Asim Shehzad, the operations director for the Perth After Hours Medical Service, said it had already affected business.

"The number of patients using our service has decreased by about 30 per cent and the reason is because we can't now directly advertise to the patients," he said.

He said he was confident his doctors had been doing the right thing but confirmed he was aware of doctors who had been writing out opioid scripts if asked.

"That was happening, I'm aware that was happening, not in our service but that was happening somewhere, I know," he said.

"With our service it's a rule that the doctors cannot prescribe any S8 [drugs of addiction] or S4 drugs, it's a rule. They don't, definitely they don't."

The Government blames ads promoting the convenience of free after-hours services for a 157 per cent increase in their use between 2010 and 2016.

In dollar terms, it represents an increased cost to the taxpayer of $155 million a year in five years.

Mr Shehzad said some doctors in the industry had attended non-urgent calls and billed Medicare for them at the higher urgent rate.

But again he said he was confident it didn't happen in his clinic.

"There were too many services who were corporate services and they actually ruined the industry," he said.

He also said patients would abuse the system by calling a doctor to their house after-hours simply to get a prescription.

"If it's a condition that cannot wait for them to go to their GP next morning, like some people are diabetic and they need a prescription at that time so that they can have their dose at night, in those cases we would issue a prescription."

"In those cases where the patient is calling for convenience, we won't."

A review of the system led to the current crackdown.

It found 63 per cent of the doctors providing after-hours services were not vocationally registered GPs, meaning they were either still in training or not members of the college of GPs.

Royal College of General Practitioners President Bastian Seidel said patients should not get a doctor with fewer qualifications just because they were taken ill in the middle of the night.

"It doesn't make any sense … (for) a trainee doctor who is on a path to become a radiologist or a pathologist to do any after hours work in general practice, it's just not his or her area of expertise," Dr Seidel said.

From now on, fully qualified GPs will get just under $130 from the Government for a genuine urgent after-hours call, but non-vocationally registered doctors will only get $100.

Australian Medical Association President Michael Gannon said free systems were always open to abuse.

"Anything that can wait until the next day, no matter how inconvenient that might be for people with their busy lives, that's not an appropriate use of the taxpayer dollar," Dr Gannon said.

He added that there was a role for after-hours services as long as the funding supporting them was appropriately targeted.