A good antihistamine is one that controls your symptoms without making you drowsy or interfering with your daily life. For most people, that means a second-generation antihistamine like cetirizine (Zyrtec), fexofenadine (Allegra), or loratadine (Claritin). These are available over the counter, work within an hour or two, and last a full 24 hours.
But “good” depends on what you’re treating, how sensitive you are to drowsiness, and whether you’re in a group that needs extra caution. Here’s how to sort through the options.
First-Generation vs. Second-Generation
Antihistamines come in two broad categories, and the difference between them is significant. First-generation antihistamines, like diphenhydramine (Benadryl) and doxylamine (Unisom), cross easily from your bloodstream into your brain. That’s what causes the heavy drowsiness these drugs are known for. It’s also why some of them are marketed as sleep aids rather than allergy medications.
Second-generation antihistamines were designed to stay mostly out of the brain. Cetirizine, fexofenadine, loratadine, and desloratadine (Clarinex) all fall into this category. They’re generally safer, cause far less sedation, and interact with fewer other medications. For everyday allergy relief, second-generation options are the standard recommendation.
How the Top Three Compare
Cetirizine, fexofenadine, and loratadine are the three most widely used over-the-counter antihistamines. They all block the same histamine receptor, but they aren’t identical in practice.
Fexofenadine (Allegra) is the least sedating of the three. In a large analysis comparing second-generation antihistamines, fexofenadine actually had a lower risk of drowsiness than loratadine. If staying fully alert is your top priority, fexofenadine is the strongest choice. The tradeoff: it can be less effective if you take it with fruit juice. Grapefruit, orange, and apple juice all interfere with how fexofenadine gets absorbed into your bloodstream, reducing its effectiveness. Take it with water.
Cetirizine (Zyrtec) is often considered the most potent for symptom relief, particularly for hives and skin reactions. It has the strongest clinical backing for chronic hives that don’t respond to standard doses. The downside is that cetirizine is the most sedating of the second-generation options. Compared to loratadine, it carries roughly 3.5 times the odds of causing drowsiness. Many people tolerate it fine, but if you’re sensitive to that effect, it may feel more like a first-generation drug.
Loratadine (Claritin) sits in the middle. It causes less drowsiness than cetirizine while offering reliable relief for seasonal allergies like sneezing, runny nose, and itchy eyes. It’s a solid all-around choice when you want something effective without much risk of feeling sluggish.
Choosing by Symptom
For seasonal allergies (hay fever), all three second-generation antihistamines work well against sneezing, itching, runny nose, and watery eyes. They’re less effective at relieving nasal congestion on their own, which is why many allergy products combine an antihistamine with a decongestant like pseudoephedrine.
For hives (urticaria), cetirizine and fexofenadine have the strongest evidence. If standard doses aren’t controlling your hives, doctors sometimes increase the dose up to four times the normal amount. Clinical data supports this approach for cetirizine, fexofenadine, and levocetirizine (a prescription version related to cetirizine), with no significant cardiac safety concerns at higher doses. However, cetirizine becomes more sedating as the dose goes up, while fexofenadine does not. Dose adjustments like these should be guided by a clinician.
For itchy eyes specifically, antihistamine eye drops containing azelastine or similar ingredients can target symptoms directly without the systemic effects of a pill.
Who Should Be More Careful
Pregnancy and Breastfeeding
Both sedating and non-sedating antihistamines are considered safe in pregnancy based on follow-up safety data. Loratadine, cetirizine, fexofenadine, and their close relatives have all been used without evidence of harm. That said, it’s better to use oral antihistamines on an as-needed basis rather than daily when possible. One specific caution: taking sedating antihistamines regularly near the time of delivery can occasionally make the baby drowsy at birth or cause mild withdrawal symptoms.
Antihistamine nasal sprays like azelastine act locally and enter the bloodstream in very small amounts, making them a reasonable option during pregnancy as well.
Older Adults
First-generation antihistamines pose real risks for people over 65. Because these drugs cross into the brain, they can cause confusion, dizziness, urinary retention, dry mouth, and blurred vision. These effects, called anticholinergic side effects, are more pronounced and more dangerous in older adults, who are already at higher risk of falls and cognitive issues. Second-generation antihistamines are a much safer choice for this group.
Interactions Worth Knowing About
First-generation antihistamines amplify the effects of alcohol, sedatives, and other medications that slow the central nervous system. Combining diphenhydramine with a glass of wine, for example, can produce much heavier sedation than either would alone.
The most notable food interaction involves fexofenadine. Unlike most drugs, where grapefruit juice causes too much medication to enter the bloodstream, grapefruit juice does the opposite with fexofenadine: it reduces absorption, making the drug less effective. Orange and apple juice have the same effect. The label on Allegra specifically says not to take it with fruit juices. Seville oranges (the kind used in marmalade), pomelos, and tangelos can cause similar problems.
Second-generation antihistamines generally have fewer drug interactions than first-generation ones, which is another reason they’re preferred for daily use.
Nasal Sprays vs. Pills
Antihistamine nasal sprays like azelastine (Astepro) deliver medication directly to the nasal lining and start working within minutes, faster than oral antihistamines. They can be especially useful if your symptoms are mostly nasal, since they reach the tissue directly rather than circulating through your whole body. Some people find the taste that drips down the back of the throat unpleasant, but the systemic side effects are minimal.
Pills are more convenient for all-over symptoms, including itchy eyes and skin reactions, since they circulate through the bloodstream. Many people with moderate to severe allergies use both: a daily oral antihistamine plus a nasal spray for breakthrough congestion or irritation.
Picking the Right One
If you need to stay sharp during the day and have mild to moderate allergies, fexofenadine or loratadine are your best starting points. If your symptoms are stubborn, particularly hives or intense itching, cetirizine tends to be more potent but may make you slightly drowsy. Taking cetirizine at bedtime can help you get the benefit without noticing the sedation.
First-generation antihistamines still have a place for short-term use, like managing a sudden allergic reaction or helping with sleep on a rough allergy night. But for daily allergy management, second-generation drugs are more effective choices with a better safety profile. If one antihistamine doesn’t seem to be working after a week or two, switching to a different one is reasonable, since individual responses vary.