Victoria’s New Cannabis Driving Laws: What Really Changed?

Recently, the Roads and Road Safety Legislation Amendment Act 2024 (Vic) was enacted, prompting misleading headlines suggesting that "cannabis is now legal to drive with." This is not true—driving with any detectable THC in Victoria remains an offence.

However, the new law does modify sentencing discretion, allowing magistrates to decide whether to disqualify a driver’s licence in certain cases involving medicinal cannabis. It does not remove penalties like fines.

What Does the New Law Actually Say?

The Roads and Road Safety Legislation Amendment Act 2024 (Vic) amends the Road Safety Act 1986 (Vic), introducing section 50(1F):

What This Means in Practice

• Driving with THC is still illegal. The amendment does not legalise cannabis use while driving—it only changes how magistrates can sentence offenders.

• Magistrates now have discretion. Previously, any conviction under s 49(1) (driving with THC present) required automatic licence disqualification. Now, if a driver used legally prescribed medicinal cannabis, a magistrate may choose not to impose a disqualification.

• Prosecutors must still prove the offence. Drivers must be over the legal THC limit (5 ng/mL in oral fluid) to be convicted, unless impairment is proven by other means.

Is Cannabis Testing Fair? Are Medicinal Users Still Targeted?

Yes, Testing is Scientifically Valid.

Cannabis undeniably impairs driving ability. Studies show that THC doubles crash risk at even low concentrations in blood or saliva. Some argue that frequent cannabis users (such as medicinal patients) may have higher THC levels without noticeable impairment, but the same could be said for alcohol tolerance in habitual drinkers—the law sets universal limits for safety reasons.

Legal THC Cut-Off in Saliva

Under AS/NZS 4760:2019 (Australia’s standard for drug testing in oral fluid), the legal THC threshold for roadside drug tests is 5 ng/mL. If a driver is below this, the case will likely fail in court unless impairment is proven otherwise.

This is similar to drink driving laws, where:

• A high-tolerance drinker may not appear impaired at 0.050 BrAC but is still over the legal limit.

• A frequent cannabis user may not appear impaired at 5 ng/mL THC, but the law assumes impairment is likely at this level.

Debunking Common Myths About Roadside Drug Testing

Myth 1: "Cannabis stays in your system for months, so tests are unfair."

Reality: Saliva tests detect active THC, not long-term metabolites.

• Urine tests look for THC-COOH, a non-psychoactive metabolite that can remain in fat stores for weeks or months after use. See: Fat people are at higher risk of reintoxication from cannabis

• Roadside drug tests only detect Δ⁹-THC, the psychoactive compound that causes impairment.

• How long does THC stay detectable in saliva?

  • Single joint (moderate dose, ~10-20 mg THC): 1-6 hours

  • Big bong hit (high dose, ~50-100 mg THC): 6-12 hours

  • Frequent heavy use: Up to 24 hours (but at this use you would never be fit to drive)

  
  

Myth 2: "Second-hand smoke can make you fail a drug test."

Reality: Passive exposure does not cause a positive result.

• THC requires direct inhalation in significant amounts to register above 5 ng/mL in saliva.

• In controlled studies, even heavy second-hand exposure in unventilated rooms ('hot boxing') rarely caused a positive test.

Final Thoughts

The Roads and Road Safety Legislation Amendment Act 2024 (Vic) does not legalise cannabis use while driving—it only allows courts to use discretion in cases involving prescribed medicinal cannabis.

While some medicinal users may feel unfairly impacted, the 5 ng/mL legal limit is based on scientific consensus, just like alcohol limits. Ultimately, if THC is in your system above the threshold, you are legally over the limit—whether impaired or not.