Alcohol, Drugs, and Impaired Driving
Impairment begins well before any legal limit. Alcohol attacks judgment and inhibition first, then reaction time, vision, and coordination - which is why an impaired driver usually believes they are fine.
The legal limit for drivers 21 and older is a BAC of 0.08%. For drivers under 21, Puerto Rico applies zero tolerance: any measurable alcohol (around 0.02% or more) is a violation. Commercial drivers have a lower threshold as well. Refusing a chemical test after arrest triggers license consequences under implied consent, because holding a license is consent to testing.
What a drink is
One standard drink - a 12 oz beer, 5 oz wine, or 1.5 oz distilled spirits - raises BAC roughly the same amount in most people. Body weight, food, medication, and fatigue change the effect. Only time removes alcohol: about one standard drink per hour. Coffee, cold showers, food, exercise, and fresh air do not sober anyone up; they only make a drunk driver feel more alert.
Drugs
Prescription and over-the-counter medicines count. Antihistamines, sleep aids, and muscle relaxants can make you drowsy, and mixing them with alcohol is dangerous even when each is used legally. Cannabis impairs reaction time and lane control. A legal prescription is never a defense for impaired driving.
Open containers
Open containers of alcohol in the passenger area of a vehicle are prohibited, and passengers can create a violation for the driver.
Trap: questions love the "I only had two beers an hour ago" setup. The correct answer is always about time, not about coffee or a shower.
Rule of thumb: if you feel anything at all, you are already too impaired to drive - arrange a sober ride before the first drink.