Drowsiness is typically considered to be the most common of all the antihistamine side effects. The majority of antihistamine medicines, many of which are available over the counter, have the ability to make a person feel very sleepy. In addition to sleepiness, antihistamines are also capable of causing urination difficulty along with dryness of the mouth and eyes. Older antihistamines, which are frequently referred to as first-generation antihistamines, are much more likely to cause these side effects. Many people who take second- and third-generation antihistamines do not experience antihistamine side effects at all.
Antihistamines may not affect every person in the same way, and some people are naturally more sensitive to them than others. People who are incredibly sensitive to antihistamines should use caution when taking them. Driving and operating any type of heavy machinery should typically be avoided by people who frequently experience antihistamine side effects. Alcohol and antihistamine use do not usually mix well because alcohol can make a person's drowsiness worse when he is taking antihistamines. Most doctors tell patients to take their antihistamines before going to bed rather than throughout the day, particularly if their patients are sensitive to the medication.
There are some people who should avoid using antihistamines unless their doctors prescribe them. Antihistamines have not been proved safe for use in pregnant women, and doctors typically advise their pregnant patients against taking them. Men who suffer from an enlarged prostate may also need to avoid antihistamine use unless their doctors recommend them. People who tend to retain urine may also need to avoid antihistamines because the drug by itself tends to cause urine retention, and it could make a person's symptoms much worse if she already suffers from that problem. Doctors do occasionally prescribe antihistamines for children, but normally do so with great caution; antihistamines may not be prescribed at all for babies and toddlers.
In spite of the potential antihistamine side effects that some people experience, antihistamines are often very helpful for controlling allergy symptoms. The fact that antihistamines can cause drowsiness might actually be considered a benefit to a person who is having trouble sleeping due to a cold or allergies. Antihistamines are considered very useful for helping with runny noses, sneezing, and itchy eyes and nose resulting from allergies. People who have itching that resulted from other causes, such as insect bites or eczema, might also find relief from antihistamine use. A person who has ever had any serious health problems or is on some type of prescription medication should probably talk to his doctor before taking antihistamines to be sure they are safe for him.