Antihistamines are a common class of medications used to alleviate the uncomfortable symptoms associated with allergies, such as sneezing, runny nose, and itching. They are also frequently included in over-the-counter cold and sleep aids to help manage various cold symptoms. As with many medications, people often notice changes in their body’s normal functions when starting these drugs. A frequent concern is whether these allergy medications directly increase the need or urge to urinate, making a person pee more often than usual. This article examines the relationship between antihistamines and changes in urinary patterns.
Antihistamines and the Question of Increased Urination
The direct answer to whether antihistamines cause polyuria, which is the medical term for producing an abnormally large volume of urine, is generally no. Antihistamines do not function as diuretics, meaning they do not directly signal the kidneys to increase urine production by affecting fluid and salt balance. The perception of needing to urinate more frequently may sometimes be an indirect effect of the medication. Many antihistamines, particularly older types, can cause a side effect known as xerostomia, or dry mouth. To combat this uncomfortable sensation, individuals often increase their fluid intake significantly, which naturally results in more frequent trips to the bathroom.
Anticholinergic Effects and Urinary Retention
The primary and most widely recognized effect of many antihistamines on the urinary system is actually the opposite of peeing more: the risk of urinary retention. This condition involves difficulty or inability to empty the bladder completely. The mechanism behind this is the medication’s anticholinergic properties, which means they block the action of the neurotransmitter acetylcholine. Acetylcholine signals the detrusor muscle in the bladder wall to contract during urination. By blocking the muscarinic receptors, antihistamines impair the bladder’s ability to contract effectively, preventing the forceful contraction required to push urine out. If the detrusor muscle cannot contract properly, the bladder remains full, leading to incomplete emptying, especially in individuals with pre-existing conditions like an enlarged prostate.
Differences Between First and Second-Generation Antihistamines
Antihistamines are broadly classified into two generations based on their chemical structure and side effect profiles. First-generation antihistamines, such as diphenhydramine and chlorpheniramine, are known for having much stronger anticholinergic properties. These older drugs readily cross the blood-brain barrier, which is why they commonly cause sedation and other wide-ranging side effects, including urinary issues. The second-generation antihistamines, which include drugs like cetirizine, loratadine, and fexofenadine, were developed to be more selective. They minimally cross the blood-brain barrier, resulting in a much lower degree of anticholinergic activity and significantly reduced risk of urinary retention.
When to Consult a Healthcare Provider
While minor changes in fluid intake and subsequent urination frequency are usually harmless, certain urinary symptoms require immediate medical attention. If you experience a sudden, noticeable difficulty in starting to urinate or feel a persistent sensation of incomplete bladder emptying, you should contact a healthcare provider promptly. These symptoms could indicate urinary retention, which can lead to complications if left unaddressed. Other concerning signs include pain or burning during urination, the presence of blood in the urine, or a new onset of fever or chills alongside urinary changes. It is important to remember that severe urinary symptoms are not a normal or expected part of taking antihistamines.