Allergy Medications: Antihistamines and Decongestants Risks You Can't Ignore

Every year, millions of people reach for antihistamines and decongestants to chase away sneezing, stuffy noses, and itchy eyes. These medications are everywhere - on supermarket shelves, in pharmacy aisles, even in convenience stores. They’re cheap, easy to grab, and feel like a quick fix. But here’s the truth most people don’t talk about: antihistamines and decongestants aren’t harmless. They carry real, sometimes dangerous, risks - especially if you’re over 65, have high blood pressure, or are taking other meds.

How These Meds Work (And Why That Matters)

Antihistamines block histamine, the chemical your body releases during an allergic reaction. That stops sneezing, runny nose, and itching. But not all antihistamines are the same. First-generation ones like diphenhydramine (Benadryl) and doxylamine (Unisom) cross into your brain. That’s why they make you drowsy - sometimes so badly you can’t drive or operate machinery. Second-generation ones like loratadine (Claritin) and cetirizine (Zyrtec) don’t cross the blood-brain barrier as easily, so they’re less likely to knock you out. But they’re not risk-free.

Decongestants like pseudoephedrine (Sudafed) and phenylephrine shrink swollen blood vessels in your nose. That’s how they clear congestion fast. But they don’t just shrink blood vessels in your nose. They shrink them everywhere - including in your heart and brain. That’s why your heart might race, your blood pressure spikes, or you feel jittery and anxious.

The Hidden Dangers of First-Generation Antihistamines

If you’re over 65, you need to hear this: diphenhydramine and doxylamine are on the Beers Criteria list of medications older adults should avoid. Why? Because they’re anticholinergic. That means they block a brain chemical called acetylcholine, which controls memory, muscle movement, and bladder function.

In older adults, this leads to:

• Confusion and memory problems - up to 50% more likely
• Blurred vision and dry mouth
• Constipation and trouble urinating
• A 300% higher risk of falling

AARP’s 2022 report found that seniors on these meds are far more likely to end up in the ER after a fall. And it’s not just about drowsiness. Even if you feel fine, your balance and reaction time are still impaired. One study showed that taking diphenhydramine at night increases fall risk the next day - even if you don’t feel sleepy.

And here’s something few people know: stopping these meds suddenly can cause severe itching. It’s called antihistamine withdrawal pruritus. You stop taking Benadryl, and your skin starts burning - no rash, no bug bites. Just intense, unexplained itching that lasts days. It’s rare, but real.

Decongestants: The Silent Blood Pressure Threat

Pseudoephedrine and phenylephrine are sold as if they’re safe for everyone. But they’re not. If you have high blood pressure - and nearly 116 million American adults do - these meds can push your numbers into dangerous territory.

Mayo Clinic data shows decongestants can raise systolic blood pressure by 5-10 mmHg. That might sound small. But for someone with uncontrolled hypertension, that spike can trigger a heart attack or stroke. And it doesn’t take much. One pill, taken with coffee or an energy drink, can be enough.

Nasal sprays like oxymetazoline (Afrin) seem safer because they’re local. But they’re not. Using them for more than three days? You’ve got a 50% chance of rebound congestion - your nose gets worse after you stop. Now you’re stuck in a cycle: spray to feel better, stop and feel worse, spray again. It’s called rhinitis medicamentosa. And it’s hard to break.

Combination Products Are a Minefield

You see them everywhere: “All-in-One Cold & Allergy Relief.” “Nighttime Sinus & Flu.” “Maximum Strength Congestion & Cough.”

These products mix antihistamines, decongestants, painkillers, and cough suppressants. And that’s the problem. You might not realize you’re taking two doses of acetaminophen (Tylenol) - one in the cold med, one in the painkiller you took earlier. The daily limit is 4,000 mg. Go over that, and you risk liver failure. You don’t need to overdose dramatically. Just taking an extra tablet a day for three days can do it.

And then there’s the antihistamine added to the mix. If you have an enlarged prostate - common in men over 50 - that antihistamine can make it impossible to pee. You end up in the ER with a full bladder.

Who Should Never Take These Meds?

The NHS and FDA list clear red flags. Don’t take decongestants if you have:

• High blood pressure
• Heart disease
• Diabetes
• Thyroid problems
• Enlarged prostate
• Glaucoma
• Liver or kidney disease

Antihistamines aren’t safe either if you have:

• Seizure disorders
• Bladder problems
• Severe dry mouth or constipation

And if you’re pregnant? The American College of Obstetricians and Gynecologists says avoid decongestants in the first trimester. For antihistamines, stick to second-generation options like loratadine - and only under a doctor’s guidance.

Medication Interactions That Can Kill

People don’t think about drug interactions with OTC meds. But they should.

Taking a decongestant with an SSRI antidepressant (like sertraline or fluoxetine)? You’re risking a hypertensive crisis - blood pressure can shoot over 180 mmHg. That’s a medical emergency.

Mixing antihistamines with alcohol? You’re doubling the sedation. That’s why older adults on Benadryl and a glass of wine are four times more likely to fall.

And don’t forget MAOIs - older antidepressants like phenelzine. Taking a decongestant within two weeks of stopping one of these can cause a deadly spike in blood pressure. That’s why the Mayo Clinic says: never mix them.

Even energy drinks are a problem. Caffeine + pseudoephedrine = racing heart, panic attacks, chest pain. Rutgers University’s poison control center saw a 25% jump in calls from young adults mixing OTC allergy meds with energy drinks in 2022.

What to Do Instead

If your allergies last more than 10-14 days, it’s not allergies anymore. It’s probably a sinus infection - and antihistamines can make it worse by thickening mucus. Mayo Clinic says 25% of patients with sinus infections get worse on antihistamines.

Here’s what actually works:

• Saline nasal rinses - safe, cheap, and effective
• Intranasal corticosteroids (like fluticasone) - better than decongestants for chronic congestion
• Allergy shots or tablets - for long-term relief
• Humidifiers and air filters - reduce triggers at home

And if you need something fast? Try a second-generation antihistamine like loratadine. No drowsiness. No brain fog. Just relief.

When to See a Doctor

You don’t need to suffer. But you also don’t need to guess.

See your doctor if:

• Your symptoms last more than two weeks
• You’re using OTC meds more than twice a week
• You have high blood pressure, heart disease, or are over 65
• You’re taking any prescription meds
• You’ve had side effects like rapid heartbeat, confusion, or trouble urinating

Pharmacists can help too. The American Pharmacists Association says 78% of OTC medication errors could be avoided with a simple chat at the counter. Ask: “Is this safe for me?” It’s not a waste of time. It could save your life.

The Bottom Line

OTC doesn’t mean risk-free. Antihistamines and decongestants are powerful drugs. They can help - but they can also hurt. If you’re over 65, have heart issues, or take other meds, you’re at higher risk. And if you’re using them long-term, you’re probably making things worse.

Stop treating symptoms like they’re just annoying. Start treating them like they’re signals. Your body is telling you something. Maybe it’s allergies. Maybe it’s something else. Either way, don’t reach for the bottle without asking: Is this really safe for me?