Antihistamines are the most common allergy medicine. They ease sneezing, itching and a runny nose by blocking histamine. This guide compares the main types, explains when to take them for the best effect, and covers side effects, safety tips and use in children.
It draws on the American College of Allergy, Asthma and Immunology (ACAAI), the FDA and MedlinePlus. It is general information, not medical advice.
Key takeaways
- Antihistamines relieve sneezing, itching and a runny nose, but do little for congestion (ACAAI).
- Newer (second-generation) types usually cause little or no drowsiness (ACAAI).
- They work best started before symptoms, and taken regularly for a few days (ACAAI).
- The FDA warns of rare, severe itching after stopping long-term cetirizine or levocetirizine (FDA).
- They don’t treat anaphylaxis. That needs epinephrine (ACAAI).
How antihistamines work
When you breathe in pollen, dust or another allergen, your body releases histamine, the chemical mainly responsible for sneezing, itching and a runny nose. Antihistamines counter its effects (ACAAI). They relieve symptoms; they don’t cure the allergy.
They work best before symptoms start. A dose taken early can prevent the need for many later doses, and taking one regularly for 3 to 4 days builds up blood levels so it works better (ACAAI). That is why many people start a daily antihistamine just before their pollen season. Check yours on our pollen near me by city pages.
Types of antihistamines
| Type | Drowsiness | Best for |
|---|---|---|
| First-generation pills and liquids | More likely; can impair driving even the next day | Short-term use when drowsiness isn’t a problem |
| Nasal sprays (azelastine, olopatadine) | Can cause sleepiness in some people | Fast relief, used as needed; can also help congestion and postnasal drip |
| Second-generation pills (newer) | Little or none for most people | Daily use through the allergy season |
Short-acting antihistamines can be taken every 4 to 6 hours, and timed-release ones every 12 to 24 hours (ACAAI). Compare options in antihistamine pills vs. nasal sprays and Zyrtec vs. Claritin vs. Allegra.
What they treat, and what they don’t
Antihistamines relieve (ACAAI):
- Eye itching, burning, tearing and redness
- Itchy skin, hives and eczema
- Sneezing and an itchy, runny nose
They do little for a stuffy nose. Nasal steroid sprays are the most effective treatment for allergic rhinitis (MedlinePlus), and decongestants can help short-term. For food allergies, antihistamines may ease mild hives, but they do not stop a severe reaction. Anaphylaxis needs epinephrine (ACAAI).
Side effects
Older (first-generation) antihistamines can cause drowsiness and impair performance, even the day after a bedtime dose, so don’t drive or use machinery until you know how one affects you (ACAAI). A frequent side effect is dryness of the mouth, nose and eyes. Men with an enlarged prostate may have urinary problems (ACAAI).
If you use cetirizine (Zyrtec) or levocetirizine (Xyzal) daily for months, know that in 2025 the FDA required a warning about rare but severe itching after stopping long-term use (FDA). See Xyzal vs. Zyrtec.
Safety tips
- Alcohol and tranquilizers add to drowsiness (ACAAI).
- Don’t take more than one antihistamine at a time unless prescribed (ACAAI).
- For an overdose, call Poison Control at 1-800-222-1222, or 911 if the person has collapsed or has trouble breathing.
- Read the Drug Facts label, since different products can contain the same ingredient (FDA).
- Talk to your doctor first if you are pregnant or breastfeeding, or have glaucoma or an enlarged prostate (ACAAI).
Antihistamines for children
Some over-the-counter allergy medicines are approved for children as young as 6 months, but not all. Children can be more sensitive to side effects such as excitability or drowsiness, so check the age limits and dosing on the label (FDA). See our children’s allergy guide.
What actually helps
We may earn a commission from qualifying purchases. Read our affiliate disclosure.
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 AmazonSaline 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 AmazonDust-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 AmazonFrequently asked questions
Which antihistamines are least likely to make me drowsy?
Newer (second-generation) antihistamines generally cause little or no sleepiness (ACAAI).
Can I take an antihistamine every day?
Timed-release antihistamines suit people who need daily medicine (ACAAI). If you use cetirizine or levocetirizine for months, talk to your doctor about the FDA’s itching warning (FDA).
Why did my antihistamine stop working?
Some people find an antihistamine becomes less effective as the season worsens or their allergies change. An allergist may suggest a different type or strength (ACAAI), or immunotherapy.
Do antihistamines help a stuffy nose?
Not much. Nasal steroid sprays or short-term decongestants work better (MedlinePlus).
Related reading
Local pollen and allergist guides
Pollen seasons and triggers change by city. See what is in the air near me and where to find an allergist.
City pollen guides
State guides
Sources
Originally written by Madiha Ather Hashmi (2020). Updated November 2026 with current sources.
This page is for general information only and is not medical advice. Talk with your doctor or pharmacist about your symptoms and before starting, stopping or combining any medicine.