How Allergy Medicine Can Cause Constipation
Certain allergy medications can cause constipation due to their anticholinergic properties. Anticholinergic agents block acetylcholine, a crucial neurotransmitter that controls involuntary muscle movements, particularly in the gastrointestinal tract. When these medications interfere with acetylcholine, the smooth muscles lining the intestines become less active. This reduced activity slows peristalsis, the rhythmic contractions that propel waste through the digestive system. As a result, stool transit time through the colon increases, allowing more water to be absorbed, making stool harder, drier, and more difficult to pass, leading to constipation.
Common Allergy Medications and Their Constipation Risk
The likelihood of constipation from allergy medication depends on the specific antihistamine. First-generation antihistamines are more frequently associated with this side effect due to their stronger anticholinergic properties. These older medications readily cross the blood-brain barrier, affecting both central and peripheral systems. Common examples include diphenhydramine (Benadryl), chlorpheniramine, clemastine, and promethazine.
In contrast, second-generation antihistamines generally pose a lower risk of constipation. These newer medications are more selective, primarily targeting peripheral histamine receptors with reduced ability to cross the blood-brain barrier. This minimizes their anticholinergic effects on the gut. Examples include loratadine (Claritin), cetirizine (Zyrtec), and fexofenadine (Allegra). While less common, mild gastrointestinal disturbances, including constipation, have been reported.
Strategies for Managing Constipation from Allergy Medicine
Individuals experiencing constipation while taking allergy medication can adopt several strategies. Increasing fluid intake is a primary recommendation, as adequate hydration keeps stools softer and easier to pass. Aim for at least eight glasses of water daily. Incorporating more dietary fiber into meals is another effective approach. Fiber adds bulk to stool, promoting regularity, with good sources including fruits, vegetables, whole grains, and legumes.
Regular physical activity also supports healthy bowel function. Even a daily walk can stimulate intestinal movement. If lifestyle adjustments do not provide sufficient relief, discuss medication options with a healthcare professional. They might suggest switching to a different allergy medication, such as a second-generation antihistamine. Do not discontinue any prescribed medication without medical guidance.
For temporary relief, over-the-counter laxatives or stool softeners can be considered, but use these cautiously and preferably under medical guidance. Seek medical advice if constipation persists for more than three weeks, is accompanied by severe abdominal pain, blood in the stool, or unexplained weight loss.