Four Beers, Allergy Pills, and a 20-Minute Drive Home
At 11:15 p.m. in Denver, a 34-year-old man who weighs about 160 pounds is trying to decide whether to drive home. Over the past two hours he drank four 12-ounce beers at 5% alcohol by volume. About an hour ago he also took a 10 mg cetirizine tablet for allergies; the label says it may cause drowsiness. He has eaten a full dinner. He feels 'fine,' his speech is normal, and he has no prior DUI or DWAI. His friend says he seems okay to drive. The drive is 20 minutes on city streets, and he has a valid license. He has a water bottle and plans to open the windows for fresh air. He is due at work at 7 a.m.
1. Estimate his blood alcohol concentration and explain whether he is legal to drive in Colorado.
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Four 12-ounce beers at 5% is about four standard drinks. For a 160-pound man over two hours, a rough Widmark estimate lands near 0.05%-roughly 0.04% to 0.06% depending on food, metabolism, and pour size. Colorado's DWAI threshold is 0.05%, and DUI is 0.08%. So he is not clearly legal; he is at or near the DWAI line. The 'I feel fine' test is unreliable because impairment affects judgment first. The cetirizine adds drowsiness and slowed reaction time even at a lower BAC. He should not drive.
2. How does the cetirizine change the analysis, even if his BAC is below 0.08?
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Cetirizine is a second depressant-like impairment. The label warns of drowsiness, and the effect can be stronger with alcohol; together they can slow reaction time, reduce attention, and increase lane drift even if BAC is below 0.08. Colorado law allows a DUI or DWAI based on impairment, not just a number, so the officer's observations-eyes, speech, driving, field sobriety tests-matter. Opening the windows or drinking water does not remove alcohol or the drug. Coffee does not sober a person; time does, and even time may not clear the medication's drowsiness.
3. What should he do instead of driving, and what should he expect if police stop him?
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He should leave the car and call a rideshare, taxi, or friend, or stay overnight. Waiting 20 minutes or drinking water is not enough; the body clears alcohol at roughly one standard drink per hour, and the cetirizine may still be active. If police stop him, he should comply, produce his license and insurance, and remember that Colorado's implied consent law requires a test if arrested; refusal has consequences. He should not lie about drinking or try to talk his way out. The safest plan is made before he starts the engine-not at the curb with the keys in his hand.