WA motorists could soon face tough new penalties if they are caught driving under the influence of drugs, as the State Government announces plans to introduce tougher consequences for offenders.

Key points: WA drug driving penalties are the lowest in the country

WA drug driving penalties are the lowest in the country Under the proposal, fines will double and licences will be suspended

Under the proposal, fines will double and licences will be suspended Police now have 1,500 more drug testing kits

Currently if drivers are caught drug driving they face a fine of $500 — the lowest in the country.

Under the McGowan Government's plans, this would increase to a minimum of $1,250.

Police Minister Michelle Roberts said the measures would bring Western Australia in line with the rest of the country.

The State Government also wants to introduce new offences to target motorists driving under the combination of alcohol and drugs, including stopping them from driving if illegal substances are detected.

"One of my concerns is that someone might test positive for drugs, maybe under the influence of methamphetamine and yet they can continue to drive — they face only a $500 fine," Ms Roberts said.

"We need to address that issue and make sure the penalty better reflects what the community expects, this is done elsewhere in Australia but it's not been put in place in Western Australia.

"We know that drivers are even more impaired if they are driving under the combination of the influence of alcohol and the influence of drugs."

Ms Roberts said new drug rules for motorists would bring WA in line with the rest of the country. ( ABC News: Eliza Laschon )

Under the proposal, a driver who blew 0.08 alcohol and had meth in their system would face a fine of up to $3,400 and a six-month licence disqualification.

Police conducted more than 40,000 roadside drug tests last year, with 3,845 drivers testing positive for an illicit drug.

One-fifth of the positive tests were for more than one drug, with the most common combination being for methamphetamine and cannabis.

Ms Roberts said drink driving was becoming less common while drug driving was increasing.

"Drink driving is becoming much less of a problem — there are very few people that now test positive to drink driving but we are seeing a significant number of people testing positive to drug driving," she said.

The Government said new and more efficient roadside drug testing was now being implemented.

Police officers have been provided with 1,500 drug testing kits and they can decide if further drug testing is needed.

"Police administrate vastly more alcohol tests than they do drug tests and generally they look at the drivers and make their own assessment as to whether a drug test is necessary," Ms Roberts said.

Recent figures revealed one in 10 drivers tested by police returned a positive result to illicit drugs with 89 per cent of those testing positive to methamphetamine.

The next most commonly detected drug was cannabis, followed by MDMA (ecstasy).

The new measures will be introduced into Parliament this year.