Which antihistamine is a cough suppressant?

According to the American College of Chest Physicians, first-generation antihistamine-decongestant combinations can be more effective than newer, non-sedating versions for treating coughs related to the common cold. This helps explain why certain older antihistamines, like diphenhydramine, are found in some cough and cold formulations and act as a cough suppressant.

Quick Summary

First-generation antihistamines such as diphenhydramine and chlorpheniramine can act as cough suppressants, often included in nighttime cold remedies. They work by blocking histamine and offering sedative and anticholinergic effects, which helps reduce the cough reflex. Second-generation antihistamines generally lack this antitussive effect.

Key Points

• First-Generation Antihistamines Suppress Coughs: Older antihistamines like diphenhydramine (Benadryl) and chlorpheniramine have antitussive effects, unlike their newer, non-drowsy counterparts.

• Mechanism Involves Brain and Drying Effects: Their cough-suppressing action comes from affecting the brain's cough center and their anticholinergic properties, which dry up respiratory secretions.

• Diphenhydramine is a Known Cough Suppressant: Found in many nighttime cold and flu medications, diphenhydramine is specifically noted for its ability to suppress coughs and induce drowsiness for better sleep.

• Second-Generation Antihistamines Are Not Effective for Cough: Newer options like cetirizine (Zyrtec) and loratadine (Claritin) do not reliably suppress coughs because they don't affect the central nervous system in the same way.

• Combination Products Are Common: Many over-the-counter products combine an older antihistamine with a dedicated cough suppressant like dextromethorphan for multi-symptom relief.

• Side Effects Include Drowsiness: Due to their sedative properties, first-generation antihistamines can cause drowsiness and other side effects, making them most suitable for nighttime use.

First-Generation Antihistamines as Cough Suppressants

Not all antihistamines are created equal when it comes to suppressing a cough. The antihistamines known for their antitussive (cough-suppressing) properties belong to the older, first-generation class. Unlike their newer, non-drowsy counterparts, first-generation antihistamines readily cross the blood-brain barrier and affect the central nervous system. This neurological effect is what gives them a dual function: relieving allergy symptoms and suppressing the cough reflex.

Diphenhydramine (Benadryl)

Perhaps the most well-known example, diphenhydramine, the active ingredient in Benadryl and many other nighttime cold products, has been shown to have a clinically significant effect on cough. Its antitussive action is attributed to its effect on the brain's cough center, along with its notable sedative properties. By causing drowsiness, it can be particularly helpful for nighttime coughs that interfere with sleep. However, it is primarily effective for coughs related to allergies or minor irritation, and not necessarily for all types of cough.

Chlorpheniramine

Chlorpheniramine is another first-generation antihistamine found in many over-the-counter and prescription combination medications. It is often combined with other ingredients, like the traditional antitussive dextromethorphan, to provide multi-symptom relief for cold and allergy symptoms. Similar to diphenhydramine, its cough-suppressing action likely stems from its effects on the central nervous system, helping to reduce the urge to cough.

The Mechanism Behind the Cough-Suppressing Effect

For most people, a cough is not caused by a histamine-driven allergic reaction. So why do these older antihistamines work? The cough-suppressing mechanism of first-generation antihistamines is not simply due to their antihistaminic properties. The prevailing theories point to a combination of their sedative and anticholinergic effects.

1. Central Nervous System Effect: First-generation antihistamines are less selective and can affect both histamine and other receptors in the brain, including those in the brainstem's cough center. By depressing this center, they can reduce the frequency and intensity of coughing.
2. Anticholinergic Action: These older drugs have anticholinergic properties, which means they can help dry up nasal and respiratory secretions, reducing postnasal drip. This effect indirectly helps calm a cough caused by irritation from mucus dripping down the back of the throat.

First-Generation vs. Second-Generation Antihistamines

When considering which antihistamine is a cough suppressant, the distinction between generations is critical. Newer, second-generation antihistamines were developed to be more selective and to minimize side effects like drowsiness. This improved selectivity means they largely avoid crossing the blood-brain barrier and, as a result, do not have the same cough-suppressing properties as their predecessors.

Common Second-Generation Antihistamines:

• Cetirizine (Zyrtec): Primarily relieves allergy symptoms like sneezing and a runny nose, but is not a reliable cough suppressant.
• Loratadine (Claritin): Offers allergy relief with minimal sedation and does not suppress coughs.
• Fexofenadine (Allegra): Also non-drowsy and acts specifically on peripheral H1 receptors, with no noted effect on cough reflex sensitivity.

Comparison Table: Antihistamines for Cough Relief

Feature	First-Generation Antihistamines	Second-Generation Antihistamines
Examples	Diphenhydramine (Benadryl), Chlorpheniramine, Doxylamine	Cetirizine (Zyrtec), Loratadine (Claritin), Fexofenadine (Allegra)
Effect on Cough	Can suppress cough reflex, particularly for dry, irritating coughs and those caused by postnasal drip.	Do not reliably act as cough suppressants. They only treat the allergy symptoms that may trigger a cough.
Sedation	Often causes drowsiness; frequently included in "nighttime" formulas.	Non-drowsy; minimal to no sedative effects.
Side Effects	Dry mouth, blurred vision, dizziness, urinary retention.	Generally well-tolerated, with common side effects being mild headache or fatigue.
Mechanism	Crosses the blood-brain barrier, affecting the brain's cough center and offering anticholinergic effects.	Highly selective for peripheral H1 receptors; do not cross the blood-brain barrier.
Best Used For	Coughs associated with cold and postnasal drip, especially when nighttime relief and sedation are desired.	Allergy symptoms. Not for treating cough specifically unless it is directly caused by allergies.

The Role of Combination Products

It is important to note that many over-the-counter medications contain combinations of ingredients to address multiple symptoms. For example, some products combine a first-generation antihistamine like chlorpheniramine with a traditional cough suppressant like dextromethorphan. These combination products provide the benefits of both ingredients. However, it's essential to read the label carefully to understand which active ingredients you are taking and to avoid accidentally doubling up on similar medications. For instance, a daytime cold medication might have a decongestant, while a nighttime formula could add a sedating antihistamine.

Conclusion

If you are looking for an antihistamine that is also a cough suppressant, your best options are the older, first-generation drugs like diphenhydramine and chlorpheniramine. Their ability to cross the blood-brain barrier and their additional anticholinergic effects contribute to their antitussive action, making them useful for dry, irritating coughs, especially those linked to postnasal drip. Newer, second-generation antihistamines do not have this property and are only effective for coughs that are a direct symptom of allergies. Always consult with a healthcare provider or pharmacist to determine the best medication for your specific symptoms, particularly if you have other medical conditions or are taking other medications.

For more detailed information on specific combination products, see the resources available on sites like GoodRx, which offer comprehensive data on drug classes and their uses.

Note: It's important to differentiate between using an antihistamine for its cough-suppressing effects and using a dedicated antitussive like dextromethorphan. For a purely cough-related issue, a specialist antitussive may be more effective and better tolerated without the sedative side effects of older antihistamines.

Risks and Considerations

While first-generation antihistamines can be effective, they come with risks. Their sedative effects can impair your ability to drive or operate machinery. Side effects like dry mouth, blurred vision, and constipation are also common. Additionally, these older drugs are generally not recommended for young children due to safety concerns. Always follow dosage instructions and seek professional medical advice before use.

Frequently Asked Questions

Which antihistamines are known for being cough suppressants?

First-generation antihistamines such as diphenhydramine (Benadryl) and chlorpheniramine are known for having cough-suppressing effects, particularly for dry, irritating coughs associated with colds and allergies.

Why do some antihistamines suppress coughs while others do not?

The ability to suppress cough is dependent on whether the antihistamine can cross the blood-brain barrier and affect the brain's cough center. Older, first-generation antihistamines do this, while newer, second-generation antihistamines are more selective and do not.

Can I use Benadryl (diphenhydramine) for a cough?

Yes, diphenhydramine is an effective cough suppressant that works by affecting the brain's cough center and providing sedation. It is often used for nighttime cough relief due to its drowsy side effects.

Are non-drowsy antihistamines effective for coughs?

No, non-drowsy (second-generation) antihistamines like Zyrtec (cetirizine) and Claritin (loratadine) are not reliable cough suppressants. They are designed to treat allergy symptoms and do not have the same central nervous system effects as first-generation antihistamines.

What is the difference in how first- and second-generation antihistamines work?

First-generation antihistamines act on both central and peripheral H1 receptors and have anticholinergic effects that dry up secretions. Second-generation antihistamines are more selective and primarily target peripheral H1 receptors, avoiding the side effects and antitussive effects associated with the central nervous system.

Should I choose a combination medication or a single ingredient for my cough?

The best choice depends on your symptoms. If you have multiple symptoms like a cough, congestion, and runny nose, a combination product with an antihistamine and a decongestant might be beneficial. However, if your only symptom is a cough, a single-ingredient cough suppressant like dextromethorphan might be more appropriate to avoid unnecessary side effects.

Is it safe to give first-generation antihistamines to children for a cough?

First-generation antihistamines are generally not recommended for young children due to safety concerns and potential adverse effects. It is always best to consult a pediatrician or pharmacist before administering any cough medication to a child.