Yes, you can take levocetirizine as-needed for symptom relief. Levocetirizine is fast-acting and typically starts working after 1 hour. Taking levocetirizine as-needed will lead to a temporary improvement in sneezing, runny nose, and itchy eyes. However, the effects of the medication will wear off after 24 hours, so if you need continuous symptom relief it is recommended you take the medication daily.