Antihistamine

Antihistamine Overview

If you have allergies, you have probably reached for an antihistamine. These medicines counter the effects of histamine, the chemical your body releases during an allergic reaction, which is largely responsible for sneezing, itching and a runny nose (ACAAI). They relieve symptoms; they don’t cure the allergy itself.

Antihistamines are among the most widely used allergy medicines. Many are sold over the counter, others need a prescription, and they come as tablets, liquids, nasal sprays and eye drops (MedlinePlus). Newer (second-generation) products generally work well with only minor side effects (ACAAI).

Which Allergies Antihistamines Treat

Antihistamines can ease symptoms caused by many common allergens, including:

• Dust allergy
• Pollen allergy
• Dust mite allergy
• Dander allergy
• Mold allergy

Most of these are airborne triggers, which is where antihistamines help most. They also relieve itchy skin and hives (ACAAI). For food allergies, they can ease mild symptoms like hives, but they do not stop a severe reaction; anaphylaxis needs epinephrine.

Antihistamines are best at relieving these symptoms:

• Watery eyes
• Itchy skin
• Runny nose
• Sneezing and itchy nose or eyes

They don’t relieve every symptom. Antihistamines do little for nasal congestion, so decongestants or nasal steroid sprays are usually better for a stuffy nose (ACAAI). If you have shortness of breath or swelling of the lips, tongue or throat, seek emergency care instead of self-treating.

How Antihistamine Works

When an allergen such as pollen or dust enters your body, your immune system mistakes it for a threat and releases histamine and other chemicals. Histamine binds to receptors in your nose, eyes, skin and airways and triggers the familiar allergy symptoms.

Antihistamines block histamine from acting on those receptors. They work best when taken before symptoms start, and taking a daily antihistamine regularly for a few days during the season may work better than taking one only after symptoms appear (ACAAI).

That is why many allergists suggest starting a daily antihistamine shortly before your pollen season begins.

When Is It Safe To Take Antihistamine?

Most adults can use antihistamines safely. For children, always read the label: some OTC allergy medicines are approved for children as young as 6 months, but not all, and children can be more sensitive to side effects like excitability or drowsiness (FDA). Older adults may be more prone to the sedating effects of first-generation antihistamines.

If you are pregnant or breastfeeding, have glaucoma or an enlarged prostate, or have another medical condition, talk to your doctor before taking an antihistamine (ACAAI).

Antihistamines are usually taken by mouth as tablets, chewables or liquids, and are also available as nasal sprays and eye drops. Many can be bought over the counter; others require a prescription.

Is It Safe To Take Antihistamine With Other Prescription Drugs?

Often yes, but check first. Most antihistamines can be taken with other medicines, but some combinations add side effects. Alcohol, tranquilizers and other sedating medicines increase drowsiness, and you should not take more than one antihistamine at a time unless prescribed (ACAAI). Always give your pharmacist a full list of what you take.

Be especially careful and ask a pharmacist before combining antihistamines with:

• Alcohol, sleep aids, or anxiety medicines (extra drowsiness)
• Another antihistamine, including in multi-symptom cold and flu products
• Combination products that already contain a decongestant
• Any prescription medicine, if you are unsure about interactions

Read the Drug Facts label carefully, because different products can contain the same active ingredient (FDA).

Side Effects Of Antihistamine

Most side effects are mild, but tell your doctor or pharmacist if any bother you. Older (first-generation) antihistamines are more likely to cause drowsiness and can impair driving even the next day (ACAAI).

Following are mild symptoms of antihistamine:

• Drowsiness
• Dry mouth
• Trouble Sleeping
• Confusion or Hallucination
• Ringing in the ears
• Difficulty urinating

These usually aren’t emergencies, but call your pharmacist if they persist or worry you. Don’t drive or operate machinery until you know how an antihistamine affects you.

An allergic reaction to this drug is rare but can occur. Following are the severe side effects of this drug:

• Dizziness
• Trouble breathing
• Rash
• Itching
• Swelling of throat, tongue or face

An allergic reaction to the medicine itself is rare but can be life-threatening. Call 911 or your local emergency number right away if you have trouble breathing or swelling of the face, lips, tongue or throat.

Dosage

Follow the label or your doctor’s instructions. Short-acting antihistamines may be taken every 4 to 6 hours, while long-acting (timed-release) ones are taken every 12 to 24 hours and suit people who need daily treatment (ACAAI). If you use cetirizine (Zyrtec) or levocetirizine (Xyzal) daily for months, know that in 2025 the FDA warned about rare but severe itching after stopping long-term use; talk to your doctor before planning long-term use or if itching starts after you stop (FDA).

Some people take a short-acting antihistamine about 30 minutes before an expected exposure, such as a picnic during ragweed season (ACAAI). But an antihistamine will not prevent a serious reaction to a food you are allergic to.

Overdosage

Taking more than the recommended dose, or doubling up on products with the same ingredient, can cause an overdose. Signs may include:

• Severe dizziness
• Trouble standing
• Trouble Breathing
• Passing out
• And even a seizure attack can occur

If someone has these symptoms, call 911 or Poison Control at 1-800-222-1222 right away and follow their instructions.

Conclusion

Antihistamines are a safe, effective first step for many seasonal allergy symptoms when used as directed, but they relieve symptoms rather than cure allergies. If they aren’t enough, ask your doctor about nasal steroid sprays or immunotherapy. For a season-by-season guide, see spring allergies and fall allergies.

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Written by: Madiha Ather Hashmi (June 16, 2020)

This article is for general education and is not medical advice. Talk with your doctor or pharmacist about your symptoms and before starting, stopping, or combining any medicine.

What actually helps

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HEPA air purifier & filters

A portable HEPA purifier sized to the room can lower airborne particles such as pollen and dust; it only works if you replace filters on schedule. (EPA: Guide to Air Cleaners in the Home)

See the Levoit Core 300 on Amazon

Saline nasal rinse kit

Rinsing with saline can clear pollen from the nose; use distilled, sterile or boiled-then-cooled water, never plain tap water. (FDA: Is rinsing your sinuses with neti pots safe?)

See the NeilMed Sinus Rinse kit on Amazon

Dust-mite pillow & mattress covers

Allergists recommend zippered, allergen-proof encasings for pillows, mattresses and box springs, plus hot-water washing of bedding. (ACAAI: Dust Allergy)

See Hospitology zippered pillow encasements on Amazon

Antihistamine FAQs

Which antihistamines are least likely to make me drowsy?

Newer (second-generation) antihistamines generally cause little or no sleepiness, while older first-generation ones are more sedating (ACAAI).

Can I take an antihistamine every day?

Many people take a long-acting antihistamine daily during allergy season. If you use cetirizine or levocetirizine for months, discuss it with your doctor because of the FDA’s 2025 warning about itching after stopping (FDA).

Do antihistamines help a stuffy nose?

Not much. Nasal steroid sprays or short-term decongestants are better for congestion (ACAAI).

Can children take antihistamines?

Some OTC antihistamines are approved for children as young as 6 months, but not all. Check the label for age limits and dosing (FDA).

Sources

Looking for more treatment options? Find a full list of other seasonal allergy treatment options here.