Antihistamines are widely used medications to relieve allergy symptoms like sneezing, runny nose, hives, and congestion. Drugs like Benadryl, Allegra, Zyrtec, and Claritin are readily available both over the counter and by prescription in the United States. They work by blocking histamine, a chemical released by the body during an allergic reaction, which causes blood vessels to swell. However, some people are worried about a potential side effect: weight gain. This article explores the existing research to determine whether antihistamines can actually lead to weight changes.
Understanding Antihistamines
To understand the potential link between antihistamines and weight, it's important to first understand what antihistamines are and how they work. Histamine is a chemical that the body uses for various functions, including immune responses and digestion. In people with allergies, the body overreacts to allergens like pollen or pet dander, releasing excessive histamine. This leads to symptoms like a runny nose, sneezing, and itchy eyes.
Antihistamines are medicines that block the effects of histamine, thus alleviating allergy symptoms. There are two main types of antihistamines:
- H1-blockers: These antihistamines target histamine-1 (H1) receptors and are primarily used to treat allergy symptoms like hay fever, hives, and insect bites.
- H2-blockers: These antihistamines target histamine-2 (H2) receptors and are mainly used to reduce stomach acid production, treating conditions like acid reflux and stomach ulcers.
The concern about weight gain primarily revolves around H1-blockers.
The "Ask The Expert" Conclusion
Artificial intelligence answers, such as those found after a Google search, often conclude that antihistamines are more likely to cause weight gain than weight loss. This conclusion is frequently based on a limited number of studies and web-based articles.
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The NHANES Study: A Closer Look
One of the most frequently cited studies on this topic is a 2010 study published in Obesity, which utilized data from the National Health and Nutrition Examination Survey (NHANES). The study evaluated 268 adults (174 female and 94 male) who reported using prescription H1 antihistamines and compared them to 599 controls.
The results indicated that prescription H1 antihistamine users had significantly higher weight, waist circumference, and insulin concentration than the control group. Specifically, men using antihistamines were, on average, 22 pounds heavier, and women were nearly nine pounds heavier than non-users. The odds ratio (OR) for being overweight in prescription H1 antihistamine users was 1.55.
However, several limitations of this study should be considered:
- Small Sample Size: The study consisted of a relatively small subset of the larger NHANES cohort.
- Pre-existing Conditions: Participants using prescription antihistamines may have had more severe allergies or other underlying conditions that could have contributed to weight gain.
- Causation vs. Correlation: The study did not establish a causal relationship between antihistamine use and weight gain. It's possible that participants were already overweight before starting antihistamines.
- Outdated Data: The study used data from 2005-2006, meaning the types of antihistamines used may differ from those most commonly used today.
- Lack of Specificity: The study did not specify which H1 antihistamines were used by participants.
The NHANES Study: Additional Details
The racial composition of the prescription H1 antihistamine users was 80% Non-Hispanic white, 8% Non-Hispanic black, 8% Hispanic, and 4% other. The racial composition of the control group was 72% Non-Hispanic white, 10% Non-Hispanic black, 13% Hispanic, and 5% other. The most prevalent H1 antihistamines used were cetirizine (50%) and fexofenadine (37%). After adjusting for gender, prescription H1 antihistamine users had significantly higher weight (p< .001), BMI (p< .001), waist circumference (p< .001), and insulin levels (p< .005) compared to healthy controls. There were no differences in fasting glucose levels, total cholesterol, LDL or HDL cholesterol, triglycerides, and apolipoprotein B levels between groups (data not shown).
Pediatric Studies
Another study, a single-center retrospective cohort study, investigated the association between antihistamine use and obesity in children with non-alcoholic fatty liver disease (NAFLD). Of the 32 participants, 13 used antihistamines, and 19 did not. The antihistamine users experienced a mean increase in BMI percentile per year of 1.17 compared to a decrease of 0.06 in the comparison group (p = 0.0008). Antihistamine usage correlated with a mean increase in BMI z-score of 0.23 per year, as opposed to a decrease by 0.012 in the comparison group (p = 0.0016). This study found a significant increase in BMI percentile/year in both female and male antihistamine users compared to non-users.
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Proposed Mechanisms
The potential mechanisms behind antihistamine-related weight gain are not fully understood, but several theories have been proposed:
- Increased Appetite: Histamine is involved in appetite regulation, and blocking H1 receptors may lead to increased appetite and food intake. Histamine decreases hunger by affecting the appetite control center in the brain, so antihistamines could interfere with the "I'm full" signal.
- Sedation and Reduced Activity: Some antihistamines, particularly first-generation drugs like diphenhydramine (Benadryl), can cause drowsiness and lethargy, leading to decreased physical activity and reduced calorie burning.
- Metabolic Changes: Animal studies suggest that antihistamines may cause metabolic changes that contribute to weight gain.
Specific Antihistamines
The data on weight gain varies among different antihistamines. There is a lack of comparative studies with different antihistamines and a lack of data for cetirizine and fexofenadine. Increased weight is listed in the package insert for cetirizine but not fexofenadine.
- Cetirizine (Zyrtec): Some studies have suggested a link between long-term cetirizine use and weight gain.
- Fexofenadine (Allegra): There is less evidence to suggest that fexofenadine is associated with weight gain.
- First-Generation Antihistamines: Older antihistamines like cyproheptadine and diphenhydramine (Benadryl) have been linked to weight gain, with cyproheptadine sometimes used to stimulate appetite and promote weight gain.
Alternatives and Recommendations
If you're concerned about potential weight gain from antihistamines, consider the following:
- Nasal Sprays and Eye Drops: These alternatives can provide symptom relief without the potential systemic effects of oral antihistamines. Nasal corticosteroids, such as triamcinolone nasal spray or fluticasone nasal spray, do not cause weight gain and may be better options for hay fever or other allergy symptoms.
- Consult Your Doctor: Discuss your concerns with your doctor and explore alternative treatments or medications.
- Healthy Lifestyle: Maintain a healthy diet and exercise regularly to mitigate potential weight gain.
- Claritin: If you need an antihistamine for frequent allergy symptoms, Claritin might be a better choice because it has less effect on appetite and sedation.
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