This hay fever relief is effective for at least 24 hours following a single dose of cetirizine. Hide 1. Take one 10mg cetirizine tablet once a day and try to take this at the same time each day, ...

The first dose is usually taken when you wake up in the morning. If more doses are prescribed, take them as directed by your doctor, usually 4-6 hours apart. Taking this medication late in the day ...