Antihistamines are commonly used to relieve allergy symptoms and manage conditions such as hay fever, hives, and allergic reactions. While these medications are generally well-tolerated, they can have side effects in some individuals. Common side effects of antihistamines may include: 1. **Drowsiness**: Many older-generation antihistamines, such as diphenhydramine (Benadryl) and chlorpheniramine, can cause drowsiness. This can be beneficial when used as sleep aids but may be undesirable during the day. 2. **Dry Mouth**: Antihistamines can reduce saliva production, leading to a dry or parched feeling in the mouth. 3. **Dizziness**: Some antihistamines may cause dizziness or unsteadiness, which can be more pronounced in older adults. 4. **Blurred Vision**: Visual disturbances, such as blurred vision, may occur with certain antihistamines, particularly those with strong sedative effects. 5. **Headache**: Some people may experience headaches as a side effect of antihistamines. 6. **Nausea or Upset Stomach**: Antihistamines can sometimes cause gastrointestinal discomfort. 7. **Nervousness**: In some individuals, antihistamines can lead to feelings of restlessness or nervousness. 8. **Confusion (particularly in older adults)**: Some older-generation antihistamines can cause confusion or cognitive impairment, especially in elderly individuals. 9. **Difficulty Urinating**: Antihistamines can affect bladder function and lead to difficulty in urinating or incomplete emptying of the bladder. 10. **Skin Rash or Allergic Reaction**: While antihistamines are typically used to alleviate allergies, it's possible for individuals to have allergic reactions to the medication itself, resulting in a skin rash, itching, or swelling. 11. **Gastrointestinal Disturbances**: Some individuals may experience constipation, diarrhea, or other digestive issues with antihistamine use. It's important to note that the severity and likelihood of these side effects can vary depending on the specific antihistamine, the individual's sensitivity, and whether the antihistamine is a first-generation or second-generation medication. Newer, second-generation antihistamines, like cetirizine (Zyrtec), loratadine (Claritin), and fexofenadine (Allegra), are designed to be less sedating and have a reduced likelihood of causing drowsiness compared to older-generation antihistamines. Always read the label, follow dosing instructions, and consult with a healthcare provider or pharmacist if you have concerns about potential side effects or interactions with other medications.