All but one of the backpackers involved in a mass drug overdose in the Perth suburb of Victoria Park will face medical bills potentially totalling thousands of dollars.

Nine foreign nationals, all aged in their 20s, were rushed to three separate hospitals on Tuesday night after taking a substance which included the pharmaceutical drug hyoscine.

Eight of the group have since been released. A French man remains in Royal Perth Hospital in a critical condition.

As overseas visitors, most of the group will be required to pay the full cost of their public hospital visits as they are not eligible for Medicare.

Costs at Royal Perth Hospital start at $275 for an emergency department visit, while patients who are admitted and stay overnight face a fee of $2,586. This doesn't include the bill for any medications supplied.

Overseas visitors are also charged 100 per cent of the fee for clinicians, medical and surgical treatment in the Australian Medical Association medical services list, which could add thousands to the final bill.

A resident outside the drug overdose house in Victoria Park ( ABC News: James Carmody )

Patients treated according to 'clinical need'

A WA Department of Health spokesman said a patient's capacity to pay was not considered until after they had received necessary treatment.

"All patients presenting at emergency departments are treated first and foremost according to clinical need," the spokesman said.

"The WA health system has invoicing and debt recovery procedures in place, and any debt arising will be pursued until all reasonable avenues are exhausted."

The spokesman said the department was unable to put an approximate cost on treating a drug overdose as each case was different.

Some countries' citizens exempt from hospital fees

One nationality among the group of French, German, Italian and Morocco citizens is not required to pay for their treatment.

Italy is one of several countries which has a reciprocal health care agreement with Australia, allowing its citizens to receive Medicare benefits in Australia if they need essential treatment.

Australia also has agreements with Belgium, Finland, Ireland, Malta, the Netherlands, New Zealand, Norway, Slovenia, Sweden and the United Kingdom.

They conversely allow Australian citizens to receive free essential medical treatment in these countries.

Eight of the patients have since been released from hospital. ( ABC News: James Carmody )

Travel insurance unlikely to cover overuse of drugs, alcohol

Overseas students in Australia are required to have insurance as part of their visa requirements, but it is unknown whether the nine foreign nationals took out overseas student health insurance.

Insurance Council of Australia general communications manager Campbell Fuller said claims relating to excessive alcohol or drug taking would not generally be paid out.

"The rule of thumb for insurers is that insurance is about covering the unexpected and unknown," Mr Fuller said.

"There's an expectation by the insurer the traveller will do his or her best to not get into trouble … therefore insurers have very strong exclusions around the use or overuse of alcohol, and the use of illicit, illegal or misuse of prescription drugs."

Approximately 9,000 overseas visitors are treated in WA emergency departments each year, making up around 1 per cent of total presentations.