This chapter covers the legal limits for driving under the influence, the fact that alcohol, illegal drugs, prescription medications, and even over-the-counter drugs and cough syrup are all treated the same way under the law, and California's implied consent rule for chemical testing.
The most-tested concepts are the different BAC (blood alcohol concentration) thresholds that apply to different drivers — general adult drivers are held to a less strict standard than commercial and for-hire drivers, and drivers under 21 or on DUI probation face a zero-tolerance standard. Also expect questions on open-container rules for both alcohol and cannabis, and on the consequences of a DUI conviction or refusing a chemical test.
A common mistake is assuming "prescription" or "legal" drugs are exempt from DUI law — they are not; any substance that impairs your ability to drive safely counts. Another is forgetting that refusing a chemical test carries its own separate license penalty, independent of any DUI conviction.
Does it matter if the drug that impaired me was legally prescribed?⌄
No — the law makes no distinction between illegal drugs and medications from a doctor or pharmacy. If a substance affects your ability to drive safely, driving under its influence is illegal.
Why are the BAC limits different for different types of drivers?⌄
California sets a stricter (lower) limit for drivers who are under 21, on DUI probation, or driving commercially or for hire, because of the added responsibility or heightened risk in those situations — always check which category applies to you.
What happens if I refuse a chemical test after being lawfully arrested for DUI?⌄
Under California's implied consent law, refusing a breath, blood, or urine test after a lawful DUI arrest results in its own license suspension or revocation — separate from whatever happens with the DUI charge itself.