Cetirizine

What it is

Cetirizine is a second-generation antihistamine that blocks the H1 receptor, preventing histamine released during an allergic reaction from producing itching, sneezing, a runny nose and hives. It acts on the periphery but crosses into the brain somewhat more than others in its class. It is used for allergic symptoms, seasonal and year-round.

Used for

• Allergy

What to know while taking it

It can be taken with or without food, and is commonly taken in the evening because drowsiness is the most frequent effect and sleeping through it is easier than working through it. Alcohol adds to that sedation and the combination is best avoided; the same caution applies to driving or operating machinery until the individual response is known. Sedatives and sleep aids compound the effect in the same way. It does not need food to be absorbed, so timing is a matter of convenience and tolerance rather than efficacy.

When to see a doctor

Daytime drowsiness heavy enough to interfere with driving, work or normal alertness is a reason to see a doctor rather than to keep adjusting the timing alone. Allergic symptoms that do not settle, or that involve swelling of the face, lips or throat, or difficulty breathing, need medical attention rather than another antihistamine.

Worth knowing

• Causes drowsiness
• Do not combine with alcohol
• Care when driving