It is best to wait until cetirizine completely leaves your body before you drink alcohol, which may take up to 40 hours (almost 2 days). This is because alcohol can increase the nervous system side effects of cetirizine such as dizziness, drowsiness, and difficulty concentrating. Some people may also find it difficult to think or make good judgements. This calculation is based on the half-life of cetirizine, which is 8.3 hours, and experts say it takes 4 to 5 half-lives for a drug to fully leave your body which works out to 33 to 40 hours.