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Doctor insights on: What Is The Average Time Needed For An Antihistamine To Begin To Work

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What is the average time needed for an antihistamine to begin to work?

What is the average time needed for an antihistamine to begin to work?

45-90 minutes: Antihistamines taken by mouth begin to work in about an hour but may take longer if you've just eaten. Antihistamine nasal sprays (astepro, patanase) begin to work in 30 minutes. An antihistamine injection, usually diphenhydramine, sometimes given for a severe allergic reaction or anaphylaxis begins to work in a few minutes. ...Read more

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Dr. Paul Carter
630 doctors shared insights

Antihistamine (Definition)

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


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What is the best time to take an antihistamine?

What is the best time to take an antihistamine?

Any time: You can take antihistamines any time of the day.Take them same time of day everyday. ...Read more

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How many milligrams of antihistamine can a person take at one time?

How many milligrams of antihistamine can a person take at one time?

Unclear: Different antihistamines have different potencies. 10 mg of Zyrtec is equivalent to 180mg of Allegra (fexofenadine). Mg doseage as in all medicines are drug specific. In regard to toxic levels, each has it's own known limit. However too much antihistamine can lead to deadly arrythmias/ Please use the recommended dose. ...Read more

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What is the highest dosage of antihistamine that one person can take at one time?

What is the highest dosage of antihistamine that one person can take at one time?

Antihistamines: Safety of high dose medications is often unknown. Our experience comes from case reports of persons who intentionally or accidentally consumed unusually excessive quantities. When Claritin (loratadine) was first investigated, safety studies were done at 40 mg (4 times the current recommended dose). We take 10 mg because effectiveness is not significantly different between 10 mg and 40mg. ...Read more

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I am about to take an antihistamine for the first time but my friends tell me to use it before bedtime. Will I still feel the effects the next day?

Depends on the med: Some antihistamines are more sedating than others. Medications like Benadryl (diphenhydramine) can definitely cause sedation. Newer antihistamines like Allegra and Claritin are non-sedating and Zyrtec is sedating in roughly 10-20% of patients. ...Read more

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Can i take citalopram and antihistamine at the same time?

"Can I": "I" is the catch in your question. I can't give advice to you in particular. The answer depends on your other known conditions and the Celexa dose. For an otherwise healthy person, 30mg daily of Celexa or less plus an antihistamine at standard dose carries a low risk for heart problems. Discuss with your doctor and the pharmacist dispensing the Celexa before going forward with the combo. ...Read more

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Can i take citalopram and antihistamine at the same time?

Can i take citalopram and antihistamine at the same time?

Probably: This combination is usually safe, but individual factors may influence this. Consult your doctor to deal with your specific circumstances. ...Read more

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Do people take an antihistamine and a corticosteroid at the same time?

Do people take an antihistamine and a corticosteroid at the same time?

Yes: And the treatment should be under medical guidance, dosage of steroids need to be dictated by your treating physician. ...Read more

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Allergy shots or antihistamine pills which works better?

Allergy shots or antihistamine pills which works better?

Allergy shots: antihistamines only cover up symptoms and don't cure anything. Allergy shots treat the cause and that is why with successful immunotherapy you can get rid of antihistames. One complication of nasal allergy treated symptomatically is development of asthma. On the other hand if you treat the cause you prevent complications ...Read more

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When is the best time to take an antihistamines for an allergy? Why?

When is the best time to take an antihistamines for an allergy? Why?

It depends: It depends on the antihistamine and when you are exposed to the cause for your allergies. Antihistamine pills generally take at least 30 minutes to two hours to take effect and peak hours later. Pollen levels are highest in the morning, but if you are exposed to other allergens such as animal dander or dust, those levels would affect you at night. Take it a few hours before your worst time. ...Read more

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I am anxious, stressed or even excited. I have heard that antihistamines work well to prevent this, is this true?

I am anxious, stressed or even excited. I have heard that antihistamines work well to prevent this, is this true?

Yes: Antihistamines can be helpful for treating anxiety. Psychiatrists will commonly prescribe Hydroxyzine pamoate for the treatment of anxiety that is technically an antihistamine. This medication is safer than many alternatives for anxiety and can be used in an as needed way. Talk with your physician for more information. Stay safe! ...Read more

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Will out of date antihistamine tablets still work ?

Maybe: Medications that have passed the expiration may still work, but the pharmaceutical manufacturer cannot guarantee their effectiveness. The longer the medication is out of date, the more likely they are less effective. ...Read more

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For what length of time will antihistamines remain active in the body?

For what length of time will antihistamines remain active in the body?

Depends : It depends on the antihistamine. There are fast acting antihistamines such as Benadryl (diphenhydramine) and Atarax also known as Diphenhydramine and Hydroxyzine that generally last approximately 6 hours. Longer acting antihistamines such as Allegra and zyrtec also known as fexofenadine and Cetirizine generally last approximately 24 hours. ...Read more

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How long does it take antihistamines to get out of your system? I was told not to take any for 1 week, but inadvertently did. Is 5 days enough time?

How long does it take antihistamines to get out of your system? I was told not to take any for 1 week, but inadvertently did. Is 5 days enough time?

Yes: most antihistamines clear within 2 -3 days or less, 1 week is a precautionary measure to make sure that your system is clear, that's mainly if are going to be skin tested for allergies to either drugs, inhalants (such pollens), or foods extracts ...Read more

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How long until an antihistamine works on post nasal drip?

THEY WON'T HELP MUCH: Other than drying it up a bit and thickening it, which can cause cough. The key in trying to eliminate postnasal drip is to cut the inflammatory or environmental response that it is caused by. ...Read more

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I am on prednisolone, hydroxycloroquine and an nsaid. Can i take antihistamine at the same time?

I am on prednisolone, hydroxycloroquine and an nsaid.  Can i take antihistamine at the same time?

Maybe but it depends: I can't answer your question exactly b/c you didn't specify NSAID or antihistamine. Check out both www.Online.Epocrates.Com & www.Drugs.Com to check for medication interactions. Plug in what you're taking and both websites will warn you of possible interactions. They're not 100% foolproof but they're a good start. Better yet, ask whoever prescribed your meds. Always tell ur doc what you're taking! ...Read more

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Don't understand how antihistamines work for chronic hives that is due to thyroid issues and not allergies?

Chronic Urticaria CU: CU can be associated with various autoimmune disorders. Even in the absence of hypo- or hyperthyroidism, patients with thyroid autoantibodies are often poorly responsive to standard therapies and have more persistent disease. Studies have examined the use of thyroid supplementation in the treatment of CU, with mixed results. Best treatment for this condition is daily antihistamines. See Allergist. ...Read more

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