The federal government has unveiled its long-awaited rules around blood-drug concentration levels for drivers.

The draft regulation stipulates that motorists with more than two nanograms of THC (a psychoactive compound in cannabis) per millilitre of blood would be guilty of a summary offence.

However, the document doesn't state how much pot must to be consumed to reach this level.

"These offences would prohibit individuals from having certain levels of impairing drugs in their blood within two hours of driving," the draft regulation states.

A conviction for a summary offence carries a maximum penalty of six months in prison and/or a fine of $5,000.

Motorists can be charged with a hybrid offence if the Crown wanted to prove there were concentrations of THC in excess of five nanograms per millilitre of blood. Hybrid offences give prosecutors the option of pursuing a summary conviction or a conviction on an indictable offence, which can lead to a lengthy prison term. 

The document also proposes that motorists be guilty of a hybrid offence if they have any detectable levels of LSD, psilocybin, psilocin, cocaine, ketamine, methamphetamine, GHB, or 6-Monoacetelmorphine in their bloodstream.

In addition, the draft regulation includes a section on combining alcohol and drugs. It would be a hybrid offence for a driver to have 50 milligrams of alcohol per 100 millilitres of blood while having 2.5 nanograms of THC per millilitre of blood.

"It should be noted that THC is a more complex molecule than alcohol and the science is unable to provide general guidance to drivers about how much cannabis can be consumed before it is unsafe to drive or before the proposed levels would be exceeded," the draft regulation states. "It is equally challenging to provide general advice as to how long a driver should wait to drive after consuming cannabis. In this context, the safest approach for anyone who chooses to consume cannabis is to not mix their consumption with driving."

The draft regulation is proposed to be pursuant to Bill C-46, otherwise known as An Act to amend the Criminal Code (offences relating to conveyances) and to make consequential amendments to other Acts.

Earlier this year, lawyer Sarah Leamon wrote a column in on Straight.com raising serious questions about the bill's provisions around allowing police to demand breath samples "even where there is no reasonable basis for doing so".

The feds are justifying this on the basis of curbing motorists from driving while under the influence of drugs.

"However, there is nothing to indicate that the legalization of marijuana will create an upsurge in drug-impaired driving," Leamon wrote. "Other jurisdictions that have already legalized the drug have actually reported statistics that tend to indicate the opposite: there have been fewer drugged drivers on the road post pot legislation."