A survey of GPs shows that while most support the prescribed use of medicinal cannabis for their patients, they lack the training to help them.

Most Australian GPs support the use of medicinal cannabis but admit they don't know enough about prescribing it for their patients.

A survey of 640 GPs found 56.5 per cent supported medicinal cannabis being made available on prescription, with most having had at least one patient ask about it.

Most of the doctors said they would prefer GPs were trained in prescribing medicinal cannabis rather than patients having to go to a specialist, the study by the Lambert Initiative for Cannabinoid Therapeutics at the University of Sydney found.

However most GPs felt their knowledge about medicinal cannabis was inadequate, and just over a quarter felt comfortable discussing it with patients.

Eighty six per cent of the GPs rated their knowledge about medicinal cannabis as poor, while 65 per cent "strongly disagreed" that they knew how to access medicinal cannabis for patients.

Professor Iain McGregor, academic director at the Lambert Initiative, said the findings demonstrated the urgent need to educate and train GPs to prescribe medicinal cannabis.

"Despite recent policy announcements, fewer than 800 patients have accessed legal medicinal cannabis in Australia," he said.

"Part of the problem is the specialist-based model that largely excludes GPs from prescribing; most Australians know how hard it is to access specialist medical care, let alone a specialist with an interest in cannabis-based medicines.

"This situation continues to frustrate patients, many of whom simply continue to access illicit cannabis to self-medicate."

The study, published by the BMJ Open journal on Wednesday, found that GPs strongly supported medicinal cannabis being prescribed to help people cope with cancer-related pain, palliative care and epilepsy.

Support was much lower for medicinal cannabis being prescribed for depression and anxiety.

Almost half of the GPs were neutral as to whether there was sufficient overall scientific evidence for the efficacy of medicinal cannabis, the study found.

More than a quarter said they would not prescribe medicinal cannabis due to the risk of abuse and dependence.

In April, health ministers decided to streamline the process for patients wanting to get quick access to medicinal cannabis.

The commonwealth-led deal involves a single approval process under the Therapeutic Goods Administration, avoiding duplication with state authorities.

Its designed to give patients access to a "one-stop-shop" with doctors able to help patients access the medication within one-to-two days.