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What Is the Difference between Loratadine and Cetirizine?

By C.B. Fox
Updated Mar 03, 2024
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Though both loratadine and cetirizine are types of antihistamines, they are each a different chemical compound that treats the symptoms of allergies in different ways. Both of these drugs are given for the same types of allergies, and they are both effective against sneezing, nose itchiness, and watery eyes and ineffective against symptoms such as hives and systemic allergic reactions. Despite the similarities in the effects of these drugs, their chemical compositions are different and as a result, they have different effects on patients who take them.

Molecularly, these substances are structured in different ways. Loratadine is made up of 22 carbon atoms, 23 hydrogen atoms, two nitrogen atoms, two oxygen atoms and a chlorine atom. These atoms are arranged into a molecule that has a number of different branches. Cetirizine is made up of 21 carbon atoms, 25 hydrogen atoms, three oxygen atoms, two nitrogen atoms and one chlorine atom that are arranged into a long chain and connected to two molecules of hydrochloride. Though the building blocks are similar, the arrangement of these molecules allows them to fight allergy symptoms in different ways.

One of the main differences between loratadine and cetirizine are the types of side effects that patients may experience when taking them. While dry mouth and gastrointestinal discomfort are seen with the use of both of these medications, loratadine is also known to cause headaches, mouth sores, nervousness, and restlessness. Cetirizine, on the other hand, can cause drowsiness that may be severe in some patients. It is also possible for patients taking cetirizine to experience difficulty breathing, a side effect not usually seen in patients taking loratadine unless the patient is going into anaphylaxis.

Another difference between loratadine and cetirizine is the way each drug can be administered. Adults are usually given a dose of 10 milligrams once per day of either of these medications, while children over the age of two are often given half that amount. There is no established dosage of loratadine for children younger than two, whereas children between the ages of six months and two years can safely take 2.5 milligrams of cetirizine.

The long-term effects of high doses of loratadine and cetirizine are also different. In laboratory tests, cetirizine did not increase the risk of cancer or decrease fertility, even when given at doses well above the recommended maximum dose. Extremely high doses of loratadine did lead to an increased cancer risk, however, as well as a decrease in male fertility.

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Discussion Comments
By anon997573 — On Jan 27, 2017

I use antihistamine only when needed (10 to 15mg). I have food (beef) allergies and environmental allergies. I get hives (or bright red spots) on my hand when I'm exposed to a food allergen. I found Zyrtec works great and faster for both but makes me feel different (I can't explain- restless I think)... but I also have used Claritin and noticed that I feel more "normal" and environmental allergies feel like they never existed. Unfortunately Claritin is not as fast as Zyrtec, so I only use it for environmental allergies. I did feel that my body's defenses should still be allowed to work and i only try to take medicine when symptoms become an annoyance.

By anon992081 — On Aug 12, 2015

Very nice article and very nice discussion.

For those who must take loratadine, you might consider looking into desloratadine as well. I've been taking that for a long time. From what I can understand from the chemistry jargon, desloratadine is the active half of loratadine, and has fewer side effects than it. Just keep in mind the dosage should be lower.

It would also be nice to have some numbers on that increase of cancer risk.

By anon991114 — On May 27, 2015

I found centrizine to be addictive. The symptoms subside when on it but gets worse when you stop. Loratidine is different for me.

The symptoms don't get worse when I stop using it, which means I can only take it when when my allergies get bad, but not every day.

By anon990804 — On May 11, 2015

Cetirizine treats hives symptoms rather well. That why I've been on them every day for the last 7 years.

By anon971616 — On Sep 28, 2014

Gargling with Listerine (the original brownish yellow one) three or four times a day and mint steam breathing after the gargle has been a natural life saver for me. Hope this helps.

By anon966973 — On Aug 23, 2014

My son has pretty bad allergies and he is only 17 months old. I took him to an after hours clinic a few months ago for what I thought was a cold. Turns out the doctor said it was allergy's. The doctor had wrote him the Claritin. Yesterday I took my son to his pediatrician for an ear ache and runny nose which was also allergy's. The pediatrician wrote the Zyrtec.

I googled the medicines to see what the difference was to figure out which I should give him. After reading this post the bottle of Claritin will be poured down the sink. I sure did not know that it could lead to a risk of cancer. That is terrifying for me as a mother to think that I have been giving him something to help him but in the long run turn out to seriously harm him! Thanks for the encouraging article. It definitely helped me make up my mind on which medicine to use and Zyrtec has got my vote! Thanks.

By anon947456 — On Apr 25, 2014

I am also allergic to loratadine. When I took it, also I developed a rash on my entire back. I haven't tried it since, but cetirizine doesn't seem to help much. My throat is constantly itching and making me cough. My cat is also shedding now and I'm sure that has something to do with it. Does anyone have any suggestions and is it OK to try something the same day you took another allergy medication?

By anon940296 — On Mar 18, 2014

Any chance of a source for your statements on long term safety?

I'd be interested to see if the tests were directly comparable or relevant at all in the context of sensible doses used in humans.

By anon935555 — On Feb 25, 2014

I take Levocetirizine because I found out (the bad way) I was allergic to Loratadine. After taking a small dosage, I developed a massive skin rash on my back, and it didn't go away for days.

Levecetirizine alleviated my symptoms for a bit, but I've noticed increased skin sensitivity, which has ultimately led me to be in a significant amount of pain.

By anon356818 — On Nov 28, 2013

Good article. I came on here to find the difference between Loratadine and Cetirizine because I have a dust allergy and it prevents me from breathing through my nose, and when I take Loratadine it helps but when I take Cetirizine it does not work.

So I will have to take Loratadine for the rest of my life. I hope it does not give me cancer.

By Pharoah — On Sep 20, 2012

@Monika - You're right that most people need to try a few different allergy medications to see how they react and if the medications are effective.

I have seasonal allergies, and I started out taking Benadryl, but it made me too tired all the time. I tried cetirizine next, but it wasn't very effective for my allergies. Finally I tried loratadine, and that's what I still take now. It doesn't make me tired and it works really well for my seasonal allergies.

On the other hand, a good friend of mine gets really bad headaches every time she tried to take loratadine.

By Monika — On Sep 19, 2012

A lot of people think various allergy medications are interchangeable, but they aren't. As this article shows, even medications as similar as loratadine and cetirizine can have totally different side effects! If you have allergies, you really should try several allergy medications to see which one is right for you.

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