Assistant health minister Meegan Fitzharris has announced plans to establish a medical cannabis scheme as soon as practicable.

But current drug-driving laws in the ACT do not exempt medical marijuana users and do not account for level of impairment.

Roadside drug tests also pick up cannabis in the system days after use, meaning someone could lose their licence and and be hit with fines by driving even weeks after consuming marijuana.

Canberra police said this week they were concerned with the level of drug driving over the Christmas period.

ACT Policing revealed that between December 23 to January 2, 28 out of 88 drivers who were tested for drugs in the period returned positive results, pending further analysis.

"Drug driving is downright dangerous, not just to the driver but to everyone on the road around them. It's disappointing for police that these drivers aren't getting the message or taking responsibility," acting officer in charge of traffic Sergeant Ken Hedges said.

The ACT's zero-tolerance approach has come under fire from civil libertarians and criminal defence lawyers, who have expressed significant concerns over how a medicinal cannabis scheme could coexist with current laws.

Solicitor Adrian McKenna, of Ben Aulich and Associates, believed it would be "nonsense to reform one without the other" and said ACT penalties for drivers caught with cannabis in their system, even if it was a "minuscule" amount, were the country's harshest.

Mr McKenna said drivers tested by police even weeks after consuming cannabis could face a criminal conviction and six months to three years licence disqualification for a first offence.

"This is likely no matter the concentration, or if their job depends on their licence.

"Any changes to medicinal cannabis laws really should make some allowance for users to drive if the concentration of cannabis is sufficiently small and has no discernible impact on their driving."

Such a shift would bring the territory's drug-driving laws into line with drink driving legislation, which allowed drivers and riders a blood alcohol concentration up to 0.05.

Lawyer Jacob Robertson, of Sharman Robertson, said medicinal cannabis users who had to drive risked an on-the-spot, 12-hour driving ban if they were stopped by police and suspected of taking drugs.

"It would open a can of worms, should those who qualify to consume medicinal cannabis still have a valid licence or be able to drive even after 12 hours of consumption, as they will almost certainly have cannabis in their system."

Paul Edmonds, of Canberra Criminal Lawyers, said an exemption might need to apply to drivers signed up to the scheme, similar to a defence for special drivers who took medication which contained alcohol.

The dilemma was raised in NSW last year when a man who used marijuana for medical purposes was caught up in drug driving laws.

A judge found him guilty, but accepted evidence the man used cannabis for pain relief and had done so four days before driving.

The judge commented that cannabis remained in the system for some time, but the legislation did not account for impairment.

NSW government guidelines suggest it is "typically" safe to drive 12 hours after using marijuana without being picked up by mobile testing.

In the ACT, police last year caught a record number of drug drivers, prompting calls for a greater awareness about drug-driving penalties, offences and how long drugs were expected to stay in the system.

One Canberra woman started taking cannabis tincture in March, to help ease the pain caused by her chronic illness.

She told Fairfax Media that it was not taking the two or three drops of liquid at night that caused her concern about her ability to drive.

Because she wasn't smoking cannabis or trying to get high, she felt she wasn't doing anything illegal when getting behind the wheel.

"Because I know myself very well," she said. "When I wasn't using [cannabis] ... I will not able to sleep some nights but still I have to wake up and have to drive somewhere and it was, I think, more dangerous when I couldn't sleep."

Advocacy group the Canberra Med Shed said medicinal cannabis should be considered alongside other prescription drugs; users should self-monitor for impairment, and police should patrol for dangerous driving.

The Justice and Community Safety Directorate are working with ACT Health to review the implications of a medical cannabis scheme.