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Doctor insights on: Why Does Drowsiness Occur After Taking Antihistamines

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Why does drowsiness occur after taking antihistamines?

Why does drowsiness occur after taking antihistamines?

Complex: Histamine is a wake promoting neurotransmitter in the brain. Older antihistamines like Benadryl (diphenhydramine) cross into the brain and block this center allowing for drowsiness to occur. The newer antihistamines like alleges, claritin, zyrtec do not cross as easily and are less likely to promote drowsiness. ...Read more

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Dr. Marsha Davis
425 doctors shared insights

Drowsiness (Definition)

Being tired is common during pregnancy, especially in the first few months and then towards the end. Exercise, rest, and proper diet all may reduce the degree of tiredness that you feel. It may help to take ...Read more


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Does antihistamine make you drowsy?

Does antihistamine make you drowsy?

Older ones do: First generation antihistamines (benadryl, clor-pheramine, atarax) cross the blood brain barrier and cause lethargy. Second generation (allegra, claritin, zyrtec, xyzal, (levocetirizine) clarinex) cause the blood brain barrier at a much lesser amount and more targeted to the h1 receptor. ...Read more

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Can drowsiness caused by antihistamines be treated or minimized at a necesary event?

Can drowsiness caused by antihistamines be treated or minimized at a necesary event?

Yes but: A decongestant is often added to antihistamine and would counteract some of the drowsy effects but that is not a good solution. There are at least two other non-drowsy antihistamines available and steroid nasal spray actually works far better without the drowsy effect. If your only choice is a sedating antihistamine, take it an hour before you go to bed instead of the morning. ...Read more

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How can I safely test to see if an antihistamine produces drowsiness? I know even the new generation has this side effect.

How can I safely test to see if an antihistamine produces drowsiness? I know even the new generation has this side effect.

Wait until a day: when you don't have to go to school (weekend) and try it. It's the only way to know. Take the smallest dose available and see if it works. ...Read more

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Can a non drowsy antihistamine that had no side effects that I've noticed hurt you if u take 2 pills in 24hrs instead of 2?

Can a non drowsy antihistamine that had no side effects that I've noticed hurt you if u take 2 pills in 24hrs instead of 2?

No: Which antihistamine? Why using it? Sometimes, for chronic urticaria, cetirizine [Zyrtec] is dosed at 3 a day . The official dose of these is 1 a day. Allegra and claritin are also sometimes used at double or triple dose.It is best if you consult a Dr before you take doses higher than usual. ...Read more

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Why do some antihistamines make me drowsy?

Cross into brain: Older antihistamines, such as diphenhydramine, or chlorpheniramine, actually cross the barrier between the bloodstream and the brain. This causes many people to feel drowsy or sedated. It can make some people irritable, or even cause insomnia. For this reason, the "non-sedating" antihistamines were developed. These medications cause much less drowsiness, and are better tolerated. ...Read more

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What is an extra drowsy antihistamine i can ask my doctor for?

Benadryl (diphenhydramine): The classic antihistamine, which has always had a very high incidence of drowsiness. In fact, due to its safety, has been used on occasion as a sleeping aide. ...Read more

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Can Claritin (loratadine) non-drowsy antihistamine still cause drowsiness?

Can Claritin (loratadine) non-drowsy antihistamine still cause drowsiness?

Yes: Claritin is a second generation antihistamine which causes much less drowsiness than first generation antihistamine, like benadryl (diphenhydramine). The number of people who feel drowsy on Claritin is so low that it is labeled "non-drowsy". But each of us is unique. I have plenty of patients who feel drowsy on claritin, especially petite women. ...Read more

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Do histamines (not antihistamine medications) make you drowsy? Antihistamines (no decongestants added) seem to make me more alert when allergies flare

Yes: Histamine is a substance released during an allergic attack and can cause drowsiness. Some of the older generation anti-histamine agents (like benedryl) can cause drowsiness because they can pass the "blood brain" barrier and cause a direct effect on thinking. In rare cases in adults, antihistamines can cause agitation. ...Read more

Dr. Masoud Sadighpour
269 doctors shared insights

Sleepiness (Definition)

Somnolence is a condition of drowsiness and is a symptom associated with many conditions including sleep apnea, ...Read more


Benadryl (Definition)

Diphenhydramine is a sedating antihistamine which is a kind of antihistamine type drug (common ...Read more