Loratadine vs cetirizine: two common antihistamines for hay fever

During an allergic reaction, cells release histamine, which causes itching, sneezing, a runny nose, watery eyes and hives. Antihistamines block histamine from acting on its receptors, easing these symptoms. They work best when taken regularly during the pollen season, and are less effective for nasal blockage, where a steroid nasal spray is often more effective.

They do not treat the underlying allergy, and they are not a treatment for severe allergic reactions (anaphylaxis), which require emergency treatment with adrenaline and a call to 999.

Both medicines are well studied and generally well tolerated. Cetirizine has a slightly higher chance of causing sleepiness in some people, which is the reason some prefer to take it in the evening, while loratadine is generally considered to be among the least sedating. The onset of cetirizine is often a little faster, and some people find that one works better for them than the other, for reasons not easily predicted.

Side effects of both can include headache, dry mouth, tiredness and, less commonly, stomach upset. They are less likely than older antihistamines to cause marked drowsiness, but individual reaction varies, so the first dose is best taken on a day when you are not driving.

Pharmacists will ask about other medicines, liver or kidney problems, pregnancy and breastfeeding, and the age of the person taking them. Doses differ for children and may need to be reduced in people with kidney or liver impairment. People taking sedatives or other medicines that cause drowsiness, or with a history of epilepsy or urinary retention, should check before use.

In pregnancy and breastfeeding, antihistamines are used when needed under advice, and NHS guidance commonly mentions that loratadine and cetirizine are options considered, but you should confirm with a pharmacist, midwife or doctor before taking them.

NICE Clinical Knowledge Summaries on allergic rhinitis advise that oral second-generation antihistamines are suitable for mild to moderate symptoms, especially when itching, sneezing and runny nose predominate, and that an intranasal corticosteroid is more effective when nasal congestion is prominent. Loratadine and cetirizine are both named as standard options, and choice is by preference, response and side effects.

Because no single antihistamine suits everyone, trying one for a couple of weeks and then switching if there is no benefit or if side effects occur is a common approach. Combination with other treatments, such as eye drops or nasal sprays, is also usual in more troublesome seasons.

• Sneezing, itchy eyes and runny nose in the pollen season: either may be tried, taken regularly.

• You are sensitive to sedation or drive for work: loratadine is often tried first; take any new antihistamine with care.

• Symptoms are not controlled after a couple of weeks: switch to the other or ask a pharmacist about adding a nasal spray or eye drops.

• Mainly a blocked nose: ask about a steroid nasal spray, which is more effective for congestion.

• Pregnant, breastfeeding, or giving to a child: check with a pharmacist, midwife or doctor for dose and suitability.

• Swelling of the lips or tongue, wheeze, faintness or difficulty breathing after exposure: this may be anaphylaxis; call 999.

"Non-drowsy" does not mean no one gets drowsy. Antihistamines do not cure hay fever, and taking them only on the worst days is less effective than regular use in the season. And taking two different antihistamines together is not advisable without guidance.

Another misconception is that antihistamines treat all allergy symptoms. They help with itch and sneeze much more than with congestion.