Antihistamines are used to help relieve allergy symptoms in both adults and children, and are available in both over the counter and prescription strengths. Many antihistamines have a tendency to cause drowsiness, so they are also sometimes used as sleep aids. What constitutes a sufficient antihistamine dose depends primarily on the age and weight of the person taking the medication. There can also be variations in an antihistamine dose for a particular person due to preexisting medical conditions and what other medications a person takes.
Most antihistamines list recommended doses, as well as how many doses can be taken safely within a 24-hour period, on the packaging. It is not safe to assume that everyone should take one or two capsules or pills for these types of antihistamines because people with different weights can require very different doses to be safe and effective. Taking more of an antihistamine than recommended will not lead to enhanced effectiveness, and it can be extremely dangerous if it results in an overdose.
In most cases, antihistamines are safe for use in healthy children as well as adults. Children younger than the youngest age indicated on the product should not take the medication unless directed to do so by a doctor. It is important to measure liquid versions of antihistamines carefully when administering them to children to prevent an accidental overdose. Though some allergy medications indicate an appropriate dose by age, parents of children who are under or above the average weight for their ages should consult with a pediatrician or pharmacist before deciding on a sufficient antihistamine dose.
People with certain medical conditions should not take antihistamines without checking with their doctors; these drugs may be safe for these individuals, but they may require a different dosage. People with heart, liver, or kidney disease should discuss an appropriate antihistamine dose with their doctors. Individuals with glaucoma, hypertension, diabetes, or ulcers should also seek medical advice before taking these medications. While antihistamines are generally considered safe for pregnant or breastfeeding women, they should talk to their doctors about a sufficient and safe dose.
Some medications can interfere with how well antihistamines work. Other medications may also alter or intensify side effects from antihistamines. Individuals who regularly take other prescription or over-the-counter medications should consult with a medical professional before taking an antihistamine to avoid adverse interactions.
Taking an antihistamine dose that is too large could result in a dangerous overdose. Some antihistamines can be taken several times in a 24-hour period, while others are formulated for use only once per day. Fever, dry mouth, blurred vision, hallucinations, flushing, and excessive sleepiness are signs of an antihistamine overdose. Those experiencing these symptoms should seek emergency medical attention.