The first week of November is Drowsy Driving Prevention Week — to raise awareness of what you can do to reduce the risk of drifting off at the wheel.

When treating allergies or a cold, the drowsiness may be linked to the antihistamine you’re taking to control your runny nose, sneezing and itchy nose and eyes. Is there anything you can do about it?

Why Do Antihistamines Make You Sleepy?

Histamines are chemicals produced by the immune system to fight off allergens and germs. In their search-and-destroy process they cause symptoms such as runny nose, sneezing and itchy eyes. Antihistamine medications relieve these symptoms by blocking the unwanted effects of histamine.

Unrelated to the immune system, histamine is also produced in the brain, where it plays an important part in feeling awake. Antihistamines used to treat respiratory symptoms can get into the brain and interrupt this work, making you feel drowsy.

What Can You Do About It?

You can go without medicine — but suffering through the symptoms might also affect your driving.

On the other hand, some antihistamines are less likely to cause drowsiness than others. Reactions vary considerably from one person to another; what relieves your symptoms without making you sleepy may be different from what works for your friend.

When you find one that works for you, stick with it — checking chemical ingredients and dosages before changing brands or generics. On the other hand, if one doesn’t work for you, try another type.

— Newer, second-generation antihistamines such as cetirizine (Zyrtec), fexofenadine (Allegra) and loratadine (Claritin) — marketed as “non-sedating” — usually cause less drowsiness than older, first-generation medicine such as chlorphenamine (Chlor-Trimeton) and diphenhydramine (Benadryl) because they are less likely to affect the histamine produced in the brain or have other unwanted effects in the brain. Also, an added benefit is the second-generation antihistamines last longer than Benadryl. Allegra is generally the least sedating.

— Nasal spray antihistamines are also less likely to make you sleepy, since they target nasal passages directly rather than sending medicine throughout your body through the bloodstream. Regular use of an intranasal corticosteroid is not only safe but also an effective way to reduce use of antihistamines — and these do not make you drowsy. They take about seven days to start working, so you need to be patient. Ask your physician or pharmacist about using an antihistamine with the intranasal corticosteroid the first few days.

To reduce daytime drowsiness, take an antihistamine in the evening rather than in the morning: It may help you sleep, with drowsy effects wearing off by the next day. Be aware, though, that drowsiness can last longer than you might expect — and that some antihistamines can cause vivid or disturbing dreams.

Never drink alcohol when taking antihistamines; it will increase the sedation.

What About Antihistamines in Cold and Flu Medications?

What many people may not know is that cold and flu medicines marketed to treat runny nose and sneezing usually include first-generation antihistamines — the more sedating types. That’s because they are better at treating cold symptoms and drying up runny nose than the newer types.

Because of their sedating effect, cold medicines with antihistamines are labeled for nighttime use. Take this labeling seriously, as some include medications like doxylamine that are more sedating than others. Dosages may also vary, even within brands.

More is not better — read labels carefully and take only as recommended. Don’t supplement a multi-symptom cold medication with another single-ingredient antihistamine.

Be Smart, Be Aware

Smart use of medications — knowing how they treat symptoms, being aware of potential unwanted side effects and, most important, monitoring their effect on you and your health — is just one step toward controlling allergy and cold symptoms. Even more important: knowing what you are allergic to and taking steps to prevent or reduce exposure.

If your allergy symptoms tend to last longer than two weeks or are not adequately controlled with over-the-counter medications, it’s a good idea to see a board-certified allergist for a full diagnosis.

Antihistamines and intranasal corticosteroids are intended for symptom relief. If antihistamines or intranasal corticosteroids are causing side effects that make you very drowsy, there are other treatment options your doctor can offer you, like allergen immunotherapy.

Purvi Parikh, MD, is an allergist and immunologist with Allergy & Asthma Network , the leading nonprofit patient education organization for people with allergies, asthma and related conditions. She practices in New York City at Allergy and Asthma Associates of Murray Hill and New York University School of Medicine. She sits on the Board of Directors for the advocacy council of the American College of Allergy, Asthma & Immunology.

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When Allergy or Cold Medication Makes You Drowsy: How to Stay Alert originally appeared on usnews.com