Forensic Science Experts for Criminal Defence Solicitors

Call head office 01782 394929
London Office 0207 118 9001
Freephone 0800 999 7 666

The Combined Risk of Cannabis and Alcohol

Written by: Alan Baker 30th September, 2022

A study from the Insurance Institute for Highway Safety (IIHS) showed 1/3 of drivers who drink alcohol and use cannabis at the same time reported getting behind the wheel within two hours of consumption.


This raises major concern as there is evidence that shows the combination of the two worsens driving performance more than either substance by itself.

IHS reported that 1 in 10 drivers use alcohol and cannabis simultaneously over the past year, compared with 7 in 10 who reported past-year drinking.

30% of fatalities on our roadways are associated with alcohol impairment and there has been very little progress to reduce this over the past 3 decades.

IIHS also discovered that patients who were at a hospital emergency room because of a motor vehicle crash only showed an increased crash risk associated with cannabis when combined with alcohol.

IIHS surveyed more than 3,000 adult drivers across Connecticut, Delaware, New York, North Carolina, South Carolina, and Virginia on their opinions related to alcohol, cannabis, and driving.

Connecticut, New York, and Virginia all legalised cannabis for recreational uses in 2021.


In the past year:

  • 71% of the drivers within the 6 states reported drinking, 28% drove two hours or less after.
  • 24% reported using cannabis, 41% drove 2 hours or less after.
  • 11% reported simultaneously taking both substances, 33% of the drivers who reported simultaneous use reported doing so 2 hours or less before driving.

25% of men reported drinking and driving, compared with 15% of woman. 12% of men reported using cannabis and 5% reported using both substances before driving. Compared with 8% and 3% of women.

With roughly 2/3 of drivers in all the 6 states agreed to drinking and driving, there is definitely more work to do to educate the driving public about increased risk of impairment associated with alcohol, cannabis, and the combination of both.