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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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Benadryl (Definition)

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

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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Bitten by unknown insect. Redness and swelling to forarm. Marked with pen and doubled in size over 36hrs. Taking non drowsy antihistamines and icing?

Ice: Benadryl (or your choice of a non-sedating antihistamine such as Zyrtec, Claritin, or Allegra), ice, and ibuprofen is a good initial treatment for insect bites. Infection is a possible delayed complication. If you develop a boil, a discolored blister, fever, increasing pain, or other concerning signs, see a physician for an exam. ...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

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Does nasalcrom (cromolyn) cause drowsiness like some antihistamines do?

Does nasalcrom (cromolyn) cause drowsiness like some antihistamines do?

Not usually: Nasalcrom is not an antihtistamine. It is a nasal topical formulation of cromolyn, which is a mast-cell stabilizer. Essentially interfering with the release of histamine as well as other inflammatory mediators from the mast cell. ...Read more

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Besides doxylamine & diphenhydramine, what other OTC antihistamines cause drowsiness? Without a prescription.

Besides doxylamine & diphenhydramine, what other OTC antihistamines cause drowsiness? Without a prescription.

Allegra (fexofenadine): All antihistamines especially the first generation ones (benadryl, bromchlorpheniramine, CTM) can cause drowsiness when given in sufficient doses. Zyrtec (cetirizine) at the recommended dose and Loratadine at 2x the recommended dose can cause drowsiness in some people. The least likely AH to cause drowsiness is fexofenadine (Allegra). ...Read more

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Can you take generic multi symptom night time medicine with night time Thera-Flu? I don't usually get drowsy from just one dose of antihistamine. I have adhd so it's hard for me to get sleepy from that. So is it okay to take both?

Can you take generic multi symptom night time medicine with night time Thera-Flu? I don't usually get drowsy from just one dose of antihistamine. I have adhd so it's hard for me to get sleepy from that. So is it okay to take both?

No: Those preparations contain multiple drugs similar to thera-flu, the problem isn't with antihistamines only, other components could interact, or interact with whatever medicines you are on or if you are under treatment for adhd, please consult your doctor and read the labels carefully, good that you asked , always exercise caution with multiple medications, ...Read more

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Zyrtec (cetirizine) makes me very drowsy. Is this common and are there non-drowsy antihistamines that provide as effective allergy relief? Thanks

Yes: This is a common side effect of Zyrtec, but it is different for everyone. If Zyrtec makes you drowsy, you could try the other 2 common anti-histamines instead - Allegra or Claritin (loratadine). Some people have been drowsy with these medicines as well, but others have not. Best wishes. ...Read more

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What is the reason behind 1st generation antihistamine induce sleep ( by which mechanism cause sleepiness in our brain ) ?

What is the reason behind 1st generation antihistamine induce sleep ( by which mechanism cause sleepiness in our brain ) ?

Anticholinergic: First generation antihistamines block the h1 and h2 histamine receptors but also have some anticholinergic effects by partially blocking other receptors. This can lead to dry mouth, urinary retention, sedation and other side effects. This is usually dose dependent and worsens with high doses. ...Read more

Dr. Paul Carter
627 doctors shared insights

Antihistamine (Definition)

Sedating and non-sedating antihistamines prevent and treat allergic reactions, and are ...Read more


Dr. Marsha Davis
425 doctors shared insights

Drowsiness (Definition)

Drowsiness = feeling sleepy/ feeling ...Read more