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Antihistamines work by getting rid of histamines, a substance the body makes when you have an allergic reaction. Can they help you treat a cold or flu?

Colds might not be serious, but they're sure annoying! Though there's not much you can do to shorten the duration of a cold, you've got some tools at your disposal to reduce the symptoms a bit. Antihistamines — allergy medications — are often said to be able to help you deal with an itchy and runny nose. Antihistamines come in various types and are usually part of combination drugs that you can buy over the counter. 

Antihistamines: What they are and how they treat your symptoms

Antihistamines, also used to treat allergies, are medications that can help you with allergic rhinitis and other kinds of allergies. They do what they say they do — fight the histamines your body produces in response to an allergic reaction. Histamine is the substance that leads to the allergy symptoms.

Antihistamines are available in many different kinds of over-the-counter medications. First-generation antihistamines often lead to drowsiness, but more recently developed antihistamines have a lower risk of drowsiness and have fewer side effects.

Frequently used antihistamines include:

  • Zyrtec (cetirizine)
  • Benadryl (diphenhydramine)
  • Allegra (fexofenadine)
  • Claritin (loratadine).

Antihistamines can help you out if you are sneezing, suffer from nasal congestion, are itching, have watery eyes, suffer from animal allergies, or have allergy-related skin rashes (urticaria). They can also help you if you have dust mites, hives due to pollen, and swelling.

    The side effects of antihistamines

    First-generation antihistamines often make those who take them feel drowsy or sleepy, which might make it hard to concentrate or even stay awake during the day. This is why it is better to use them during the night. Besides drowsiness, frequent side effects of antihistamines include dizziness, headache, and a dry mouth.

    Among the rarer possible side effects are nausea and vomiting, constipation, nervousness, muscle weakness, a loss of appetite, chest congestion, and hyperactivity (which happens a lot in kids).

    Newer, second and third, generation antihistamines are more targeted and therefore tend to come with fewer side effects. The effects of a dose additionally last longer, meaning you can find symptom relief even if you don't take as much.

    What do antihistamines do to treat your flu or cold?

    Antihistamines function by fighting histamines. Histamines cause tissues in the nose to become itchy and swollen — symptoms you also experience when you have a flu or cold, and which antihistamines can help you take care of. 

    Histamine actually isn’t, according to scientific consensus, the main reason you have a runny nose when you have a flu or a cold. Studies also report that newer antihistamines such as loratidine (Claritin) and fexofenadine (Allegra) don’t seem to do much to relieve cold symptoms. Some of the earlier antihistames like Chlorpheniramine and brompheniramine seem to work much better.

    No one yet knows exactly why antihistamines can offer symptom relief for some people while they appear to have no effect in others. It may be that antihistamines don't work when histamine production doesn't play a role in causing your symptoms, but it's also possible that different people simply react differently to the medications.

    Do studies show if antihistamines can help with the common cold?

    There isn’t a cure for the common cold, so the best you can do is make your symptoms less uncomfortable. Antihistamines do a good job treating allergic symptoms like hay fever. Studies have been carried out to see if antihistamines can treat common cold symptoms because the nasal symptoms of hay fever are very similar to common cold symptoms.

    How well do antihistamines relieve common cold symptoms? An analysis of 18 studies in which over 4000 people participated compared antihistamines to a placebo. The study also explored whether people experienced more side effects when using antihistamines or a placebo.

    Because common colds don't tend to last more than a week to 10 days, the research was short-term. The results were interesting. Antihistamines were shown to offer better symptom relief than the placebo, however, this was not true for people who took antihistamines for longer periods of time. The research also suggested that sedating antihistamines didn't do much for sneezing and rhinorrhea.

    In short — antihistamines might make you feel better if you use them for a little while, but they won't do much for nasal clogging and mucus or sneezing in the longer term.

    So, should I take antihistamines?

    Antihistamines were designed to treat allergies rather than colds, and they obviously work much better for this intended purpose. They are, however, safe for most people. This means you could try them when you’re suffering from cold symptoms — in some cases, histamine production could be contributing to your symptoms, and in these cases, antihistamines will help. Antihistamines are most likely to make a difference if you have an itching and runny nose. Get in touch with your physician to see if antihistamines are OK for you.

    • "Common Cold: Treatment". Common Cold 11 Feb 11. National Institute of Allergy and Infectious Diseases
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