Combined Alcohol and Drug Impairment While Driving
Last reviewed: 2026 · Driviology Road Safety Education Team
Quick Answer
Combining alcohol with cannabis, prescription medication, or other drugs multiplies impairment rather than simply adding to it, and Ontario treats combined impairment as seriously as either substance alone under its impaired driving laws.
It is a common but dangerous assumption that a small amount of alcohol combined with a small amount of another substance is safer than a larger amount of just one. In reality, the combination is often more impairing than either substance alone.
Why Combined Substances Are More Dangerous
Alcohol and many drugs, including cannabis and some prescription or over-the-counter medications, both affect reaction time, judgment, and coordination. When combined, their effects on the brain do not simply add up — they can compound each other in ways that are hard to predict.
What Ontario Law Says
Ontario’s impaired driving laws cover impairment by alcohol, drugs, or a combination of both. See our full impaired driving guide for the penalties and demerit points that apply, which are the same regardless of which substance, or combination, caused the impairment.
Checking Medication Effects Before Driving
Many prescription and over-the-counter medications carry warnings about drowsiness or impaired coordination. Always check the label, and speak with a pharmacist or doctor if you are unsure whether a medication is safe to combine with driving, especially alongside any alcohol consumption.