Can Antihistamines Lead to Weight Gain? 

Dr. Christopher McGowan
October 28, 2022

The factors that contribute to the fluctuations in our body weight are complex and can be related to many different aspects of our biology and lifestyle. That’s why unexplained weight gain can be a frustrating and confusing experience, regardless of the number of extra pounds on the scale. One possible explanation for weight gain that often goes unnoticed or unexamined is the side effects of a particular medication. In recent years, as the number of people with environmental allergies continues to rise, researchers have looked into allergy medications like antihistamines as a possible culprit.   

What Are Antihistamines?      

Antihistamines are a class of drugs that are primarily used to treat the allergy symptoms of some environmental stimuli like dust, pollen, pet dander, or mold. The symptoms that present are all essentially an exaggerated immune response to a substance the body deems to be a threat. When a person with an allergy is exposed to a particular allergen, compounds called histamines are released from mast cells around the body and trigger various biological responses like the dilation of blood vessels, the contraction of smooth muscle in the lungs, acceleration of heart rate, or inflammation in affected tissues. Below are some common symptoms associated with allergies: 

  • sneezing
  • itchy eyes, nose, or mouth
  • itchy skin or rashes 
  • stuffy or runny nose
  • red or watery eyes
  • swelling 
  • hives
  • wheezing or coughing
  • shortness of breath 
  • anaphylaxis 

Both prescription and over-the-counter antihistamines are designed, as the name implies, to counter the effect of histamines and the exaggerated immune response. Antihistamines work by blocking histamine receptors on cells all around the body; this has the effect of preventing the immune response and bringing relief from the often unpleasant symptoms. The relief granted by the medication is unfortunately only temporary, however, and there is no known cure for such environmental allergies. Antihistamines, then, are used as a way of managing recurring symptoms and improving a patient’s quality of life. 

Types of Antihistamines  

There are two major subtypes of antihistamines that are based on the type of cell receptor they interact with: H1 receptor antagonists and H2 receptor antagonists. H1 blockers are mainly used for the treatment of environmental allergies, while H2 blockers are used for the treatment of gastrointestinal conditions like GERD and peptic ulcers. H1 blockers can be further divided by when they were developed. Benadryl (diphenhydramine) is probably the most well-known first generation antihistamine, and it was approved by the FDA in 1946. Second generation antihistamines were approved more recently and differ mainly in the fact that they don’t pass the blood-brain barrier; common examples include Allegra (fexofenadine), Zyrtec (cetirizine), and Claritin (loratadine).   

Side Effects of Antihistamines

Even within the main categories of antihistamines, there are many different types that work in slightly different ways. Some are meant to treat acute symptoms that pop up from time to time and can help provide relief; others are designed for chronic allergies that present at certain times of the year or regularly throughout the year. Choosing the right one can be a process of trial and error, and may involve weighing the benefits vs the side effects. Below are some common side effects of antihistamines: 

First generation

  • drowsiness
  • blurred vision 
  • dry mouth or eyes
  • headache or dizziness
  • thickening of mucus in the airways 
  • increased heart rate
  • reduced blood pressure
  • constipation
  • problems urinating 

Second generation

  • drowsiness
  • headaches
  • cough or sore throat
  • abdominal discomfort or pain
  • nausea 
  • vomiting

Do Antihistamines Cause Weight Gain?  

One other side effect of antihistamines that some people experience is weight gain, though research into this topic is still ongoing. For example, a 2010 study at Yale University used data from the 2005-2006 National Health and Nutrition Examination Survey to look at the association of prescription h1 antihistamine use with incidence of obesity. The researchers found that prescription antihistamine users had higher body weight, waist circumference, and insulin levels. Results from studies like these suggest, then, that regular use of antihistamines may indeed increase the risks for obesity, metabolic syndrome, and other obesity-related conditions.  

While there seems to be some connection between antihistamine use and weight gain, the mechanism of weight gain remains unclear. One potential explanation is related to a reduction in appetite and increase in satiety that have been observed as effects of histamine release. Since antihistamines block histamines from entering our cells, it’s possible that long-term use could lead to overeating and eventual weight gain. Antihistamines also tend to cause drowsiness and fatigue that may lower the motivation for physical activity; less physical activity can then lead to fewer calories being expended vs the level of food intake.  

The bottom line is that there is a possibility of significant weight gain when using antihistamines on a regular basis. Unfortunately, however, there is no clear answer about whether there is a specific type or dosage that is particularly likely to lead to weight gain. It has been theorized that second generation antihistamines that don’t cross the blood-brain barrier may be less likely to interfere with appetite and satiety. However, just like with other side effects of antihistamines, it may require a process of trial and error (in consultation with a healthcare provider) with different meds to figure out which one eases symptoms without gaining weight.  

Finding a Weight Loss Solution

Apart from finding a different antihistamine to manage allergy symptoms, the path to losing weight means finding a way to reduce your caloric intake, increase your physical activity level, or some combination of both. The goal is to be in a calorie deficit so that your body is forced to switch from glucose to fat stores for its energy needs. While the answer to weight loss is fairly straightforward, in practice it’s rarely that simple. In fact, most people who attempt to lose weight by adopting a new diet and adding exercise to their life typically don’t succeed in the long run. 

This is exactly why True You Weight Loss exists—to help you find a new approach for your weight loss journey that will increase the chances of having long-term, sustainable success. Rather than fad diets and punishing exercise plans, though, we offer a series of highly effective endoscopic weight loss procedures like ESG that make it easier to feel full after eating and ultimately reduce your calorie intake. To learn more about how to lose weight with True You, please contact us today to request a consultation. Freedom is waiting!

Dr. Christopher McGowan
Dr. Christopher McGowan

Dr. Christopher McGowan, MD, a leader in endobariatrics, specializes in non-surgical obesity treatments and is triple-board-certified in Internal Medicine, Gastroenterology, and Obesity Medicine. Renowned for pioneering endoscopic sleeve gastroplasty (ESG) with over 2,000 procedures, his global influence and research contributions define him as a top expert.

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