Alcohol and Drugs — Montana DMV Permit Rules & Lessons

California DUI law covers alcohol and drugs that impair safe driving, including cannabis, prescriptions, and over-the-counter medicines. Combined substances can change or intensify their effects; a driver can be impaired below a numerical BAC threshold. Notice changes in perception, judgment, coordination, and reaction. Check medication labels, plan another ride before using a substance, and understand what a DUI investigation may require. If driving ability is impaired or uncertain, do not drive; the next lesson explains BAC thresholds separately.

BAC measures alcohol in the bloodstream, but California applies different limits: 0.08 percent for ordinary adult driving, 0.04 percent for vehicles requiring a CDL or passenger-for-hire driving, and 0.01 percent for drivers under 21 or on DUI probation. More than one category may apply, so a higher threshold does not cancel a lower one. A reading below a listed threshold is not proof of safe driving; alcohol, drugs, or their combination can impair a person without a particular BAC measurement. Never treat a drink-count estimate as permission to drive.

California treats substance use during a trip and container possession as separate questions. A driver or passenger generally may not drink alcohol or use cannabis while traveling in a vehicle. Carried containers should be sealed and unopened; opened ones belong in the trunk or another non-passenger area, not an accessible glove box. Drivers under 21 face additional alcohol-possession restrictions. Limited passenger exceptions never permit impaired driving. Before travel, identify the product, container status, holder, storage location, and each person’s ability to ride or drive safely.