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

Millions of people reach for antihistamines and decongestants every fall and spring, thinking they’re just grabbing a quick fix for a stuffy nose or itchy eyes. But these common over-the-counter meds aren’t harmless snacks. They’re powerful drugs with real, sometimes serious, risks - and most people have no idea.

What You’re Actually Taking

Antihistamines like diphenhydramine (Benadryl) and loratadine (Claritin) block histamine, the chemical your body releases during an allergic reaction. That stops sneezing, runny nose, and itching. But first-gen antihistamines - the ones you find in sleep aids and cheap cold meds - don’t just stop histamine in your nose. They cross into your brain. That’s why 60% of people who take diphenhydramine feel drowsy. Some feel dizzy. Others get blurry vision or dry mouth. It’s not just annoying - it’s dangerous.

Decongestants like pseudoephedrine (Sudafed) and phenylephrine work differently. They shrink swollen blood vessels in your nasal passages. That’s why your nose clears up fast. But those same blood vessels are everywhere - in your heart, your brain, your kidneys. When you constrict them in your nose, you’re also tightening them elsewhere. That’s why your heart races, your blood pressure spikes, and you can’t sleep.

The Hidden Dangers of First-Generation Antihistamines

If you’re over 65, taking Benadryl for allergies might be one of the riskiest things you do every day. The American Geriatrics Society calls first-gen antihistamines potentially inappropriate for older adults. Why? Because they have strong anticholinergic effects - meaning they block a key brain chemical called acetylcholine. That’s fine if you’re trying to sleep. Not fine if you’re trying to remember where you put your keys.

Studies show older adults on these meds have a 300% higher risk of falling. That’s not a typo. One fall can mean a broken hip, a hospital stay, and a lifetime of reduced mobility. They also cause confusion, urinary retention (especially dangerous for men with enlarged prostates), and can make glaucoma worse. AARP found that many seniors on these meds develop anxiety, constipation, and trouble peeing - symptoms they blame on aging, not their medicine.

Even younger people aren’t safe. Mixing diphenhydramine with alcohol or sleep aids can slow your breathing to dangerous levels. Combine it with an antidepressant, and you’re playing Russian roulette with your heart rhythm.

Decongestants: The Silent Blood Pressure Killer

Pseudoephedrine doesn’t just unblock your nose - it can block your heart’s ability to relax. The Mayo Clinic says it can raise systolic blood pressure by 5 to 10 mmHg. For someone with normal blood pressure, that’s a nuisance. For the 116 million American adults with high blood pressure? That’s a medical emergency waiting to happen.

And it’s not just the pills. Nasal sprays like Afrin (oxymetazoline) seem safer because they’re local. But use them for more than three days? You’re almost guaranteed to get rebound congestion - your nose gets worse than before. Half of users develop this cycle. Then they use more spray. Then they get addicted. Then they need a doctor to break the habit.

Phenylephrine, the ingredient now in most Sudafed products, was pulled from OTC sale in Europe in 2022 because studies showed it doesn’t even work well. But in the U.S., it’s still everywhere. And it still raises blood pressure - just less predictably. That makes it more dangerous, not less.

Combination Products: The Overdose Trap

You think you’re buying one thing - a cold and allergy pill. But 68% of these products contain multiple active ingredients. One pill might have an antihistamine, a decongestant, and acetaminophen (Tylenol). That sounds efficient. Until you take another Tylenol for a headache. Or drink a soda with caffeine. Or take your blood pressure med.

Acetaminophen is the leading cause of acute liver failure in the U.S. The safe daily limit is 4,000 mg. But many people don’t realize that one “all-in-one” cold tablet has 500 mg. Take two of those, plus two more Tylenol, and you’re at 2,000 mg before lunch. By dinner, you’re at 4,000 mg. No warning signs. No pain. Just silent liver damage.

And if you’re on an SSRI antidepressant? Taking a decongestant with it can spike your blood pressure to 180 mmHg or higher. That’s not a scare tactic - it’s documented. Emergency rooms see these cases every winter.

Who Should Never Take These Meds

The NHS and FDA have clear lists. If you have:

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

- you should avoid decongestants entirely. For antihistamines, even second-gen ones like Claritin need caution if you have heart rhythm issues or are on certain heart meds.

And if you’re pregnant? The American College of Obstetricians and Gynecologists says avoid decongestants in the first trimester. Stick to loratadine or cetirizine only if your doctor says it’s safe.

What to Do Instead

You don’t need a decongestant to breathe better. Intranasal corticosteroids like fluticasone (Flonase) or mometasone (Nasonex) are more effective for chronic congestion - and they don’t raise your blood pressure. They take a few days to work, but they’re safe for long-term use.

For allergies, saline nasal rinses (Neti pots) clear out pollen and irritants without drugs. Cold compresses reduce swelling. A humidifier helps. And if your symptoms last more than 10 days? You don’t have allergies - you might have a sinus infection. Antihistamines can make that worse by thickening mucus.

When to Talk to a Pharmacist or Doctor

Most people never do. But 78% of OTC allergy medication problems could be avoided with a quick chat with a pharmacist. They know what’s in your cabinet. They know what you’re taking for your blood pressure. They know which meds interact dangerously with caffeine or energy drinks.

If you’re over 65, don’t use any first-gen antihistamine without asking. If you’re on any prescription med, check for interactions before buying anything labeled “allergy” or “cold.” If your child is under 2 - don’t give them anything without a doctor’s order. The FDA has documented deaths from these products in babies.

The Bottom Line

Allergy meds aren’t candy. They’re powerful tools - and like any tool, they can hurt you if you don’t use them right. The fact that you can buy them without a prescription doesn’t mean they’re safe. It means you have to be smarter about using them.

Don’t assume “natural” or “non-drowsy” means harmless. Don’t think “it’s just for a few days” - rebound congestion and blood pressure spikes don’t care how long you’ve used it. And don’t ignore your body’s warning signs: racing heart, dizziness, confusion, trouble peeing, or worsening congestion after three days.

If your allergies are bad enough to need daily meds, talk to an allergist. There are better, safer options. And if you’ve been popping antihistamines for years because “it’s just what I’ve always done”? It’s time to rethink that.

If you’ve been using these meds for years without thinking twice, you’re not alone. But now you know the risks. The next time you reach for that bottle, ask yourself: Is this helping me - or just masking a problem that needs real care?