Key TakeawaysWhile the class of allergy drugs called antihistamines are known for their ability to cause drowsiness, weight gain may be another side effect of some of these medications.While short-term antihistamine use likely won’t contribute to weight gain, studies do show some antihistamines have the potential to contribute to weight gain over time.Not all antihistamines cause weight gain.

Key Takeaways

While the class of allergy drugs called antihistamines are known for their ability to cause drowsiness, weight gain may be another side effect of some of these medications.While short-term antihistamine use likely won’t contribute to weight gain, studies do show some antihistamines have the potential to contribute to weight gain over time.Not all antihistamines cause weight gain.

Antihistaminessuch as Benadryl are a class of drugs commonly used to treat allergies ranging from allergic rhinitis to allergic dermatitis. While they’re known to cause side effects such as drowsiness, a lesser-known side effect is their potential to contribute to weight gain.

The reason why is because of their effect on the brain.

According toJames Walker, MD, a board-certified internist and healthcare specialist at Welzo Online Pharmacy, some antihistamines can interfere with the function of a brain region called the hypothalamus, which plays a key role in regulating energy expenditure and appetite. As a result, you may feel more fatigued or hungry when taking these medications, as well as less likely to engage in physical activity.

The type of antihistamine you choose and the frequency you take it can impact whether or not you experience weight gain. Here’s what you need to know.

Which Antihistamines May Lead to Weight Gain?

While there aren’t dedicated studies that definitively compare weight gain from different antihistamines, newer generations of H1 antihistamines are typically recommended over first-generation medicines due to a better safety profile and their lack of sedative effects. Experts say they are less likely to contribute to weight gain, too.

Anne Ellis, MD, a professor of medicine at Queen’s University in Canada, explains that first-generation H1 antihistamines, like Benadryl (diphenhydramine) and Chlor-Trimeton (chlorpheniramine), have activity on serotonin receptors that can lead to an increase in appetite and possible weight gain.

This type of activity is largely not seen in second-generation antihistamines, such as Claritin (loratadine), Zyrtec (cetirizine), and Clarinex (desloratadine)—though some research has found that the use of these medications was associated with weight gain over long-term use.

How to Prevent Weight Gain from Antihistamines

Experts aren’t sure how much weight gain antihistamines can cause, and there’s not yet enough research to make an estimate. But they emphasize that short-term use of antihistamines is generally not problematic. If long-term use is necessary, you should speak with a healthcare provider about potential side effects and risks.

Is It Safe to Take Allergy Medications Every Day?

You can also work with a registered dietitian to establish a balanced diet and healthy lifestyle alongside antihistamine use.

As a rule of thumb, Walker said the ideal diet should be rich in fruits, vegetables, lean proteins, and whole grains, while low on processed foods. Mindful eating may be important while taking antihistamines, he added, in order to be more aware of hunger and fullness cues.

Because insufficient sleep—less than six hours per night—is linked to increased appetite and food intake,prioritizing rest can also help offset the side effects of antihistamines.

What This Means For YouWhile there have been studies linking weight gain to antihistamines, further research is necessary to better understand the interactions taking place. For the most part, short-term use of antihistamines, especially second generation antihistamines, are unlikely to cause significant weight changes.

What This Means For You

While there have been studies linking weight gain to antihistamines, further research is necessary to better understand the interactions taking place. For the most part, short-term use of antihistamines, especially second generation antihistamines, are unlikely to cause significant weight changes.

3 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Recto MT, Gabriel MT, Kulthanan K, et al.Selecting optimal second-generation antihistamines for allergic rhinitis and urticaria in Asia.Clin Mol Allergy. 2017;15:19. doi:10.1186/s12948-017-0074-3Saad M, Syed S, Ilyas M, Gashev AA.Antihistamines increase body mass index percentiles and z-scores in Hispanic children.Children (Basel). 2020;7(12):305. doi:10.3390/children7120305Cooper CB, Neufeld EV, Dolezal BA, Martin JL.Sleep deprivation and obesity in adults: a brief narrative review.BMJ Open Sport ExercMed. 2018;4(1):e000392. doi:10.1136/bmjsem-2018-000392

3 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Recto MT, Gabriel MT, Kulthanan K, et al.Selecting optimal second-generation antihistamines for allergic rhinitis and urticaria in Asia.Clin Mol Allergy. 2017;15:19. doi:10.1186/s12948-017-0074-3Saad M, Syed S, Ilyas M, Gashev AA.Antihistamines increase body mass index percentiles and z-scores in Hispanic children.Children (Basel). 2020;7(12):305. doi:10.3390/children7120305Cooper CB, Neufeld EV, Dolezal BA, Martin JL.Sleep deprivation and obesity in adults: a brief narrative review.BMJ Open Sport ExercMed. 2018;4(1):e000392. doi:10.1136/bmjsem-2018-000392

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Recto MT, Gabriel MT, Kulthanan K, et al.Selecting optimal second-generation antihistamines for allergic rhinitis and urticaria in Asia.Clin Mol Allergy. 2017;15:19. doi:10.1186/s12948-017-0074-3Saad M, Syed S, Ilyas M, Gashev AA.Antihistamines increase body mass index percentiles and z-scores in Hispanic children.Children (Basel). 2020;7(12):305. doi:10.3390/children7120305Cooper CB, Neufeld EV, Dolezal BA, Martin JL.Sleep deprivation and obesity in adults: a brief narrative review.BMJ Open Sport ExercMed. 2018;4(1):e000392. doi:10.1136/bmjsem-2018-000392

Recto MT, Gabriel MT, Kulthanan K, et al.Selecting optimal second-generation antihistamines for allergic rhinitis and urticaria in Asia.Clin Mol Allergy. 2017;15:19. doi:10.1186/s12948-017-0074-3

Saad M, Syed S, Ilyas M, Gashev AA.Antihistamines increase body mass index percentiles and z-scores in Hispanic children.Children (Basel). 2020;7(12):305. doi:10.3390/children7120305

Cooper CB, Neufeld EV, Dolezal BA, Martin JL.Sleep deprivation and obesity in adults: a brief narrative review.BMJ Open Sport ExercMed. 2018;4(1):e000392. doi:10.1136/bmjsem-2018-000392

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