What's in Benadryl?: A Detailed Look at Its Active and Inactive Ingredients

October 5, 2025 •

4 min read

First-generation antihistamines like Benadryl have been a staple of over-the-counter medicine cabinets for decades. When asking what's in Benadryl, it's important to understand that the specific ingredients can vary depending on whether it's an oral medication, a topical cream, or a multi-symptom formula.

Quick Summary

Benadryl's primary active component is diphenhydramine, a first-generation antihistamine used to treat allergies, insomnia, and motion sickness. Its other ingredients vary by product type, with common additions like decongestants or skin protectants in specific formulations.

Key Points

Active Ingredient is Diphenhydramine: The key compound in most oral Benadryl products is diphenhydramine HCl, a first-generation antihistamine that provides fast-acting relief for allergy and cold symptoms.
Formulas Vary by Product Type: The specific ingredients depend on the Benadryl product, with oral tablets containing diphenhydramine, multi-symptom versions adding a decongestant, and topical creams using different active ingredients like zinc.
Benadryl Causes Drowsiness: Unlike newer antihistamines, diphenhydramine easily enters the brain, causing significant sedation that makes it useful as a sleep aid but also dangerous when driving or operating machinery.
Anticholinergic Side Effects: The medication's anticholinergic properties can lead to common side effects such as dry mouth, blurred vision, and constipation.
Warnings for Children and Seniors: Oral Benadryl should not be given to children under 6 or used to induce sleep in any child. It is also generally not recommended for older adults due to a higher risk of side effects.
Non-Drowsy Alternatives Exist: Second-generation antihistamines like Claritin (loratadine) and Zyrtec (cetirizine) offer longer-lasting allergy relief with a much lower risk of drowsiness.

Unpacking the Primary Active Ingredient: Diphenhydramine

At the core of most oral Benadryl products is the active ingredient diphenhydramine hydrochloride (HCl). This compound is a first-generation antihistamine, meaning it was one of the first types of antihistamines developed. Its main purpose is to relieve symptoms caused by allergic reactions and the common cold, including sneezing, runny nose, watery eyes, and itching of the nose or throat. Diphenhydramine is also effective for treating insomnia due to its sedative properties, and for preventing motion sickness.

How Diphenhydramine Works in the Body

To understand what's in Benadryl and why it works, it's crucial to know how diphenhydramine acts on the body. An allergic reaction is triggered by the body's immune system releasing a substance called histamine. Histamine binds to H1 receptors in the body, causing the classic allergy symptoms. Diphenhydramine works by blocking these H1 receptors, which prevents histamine from triggering these effects.

Unlike newer, second-generation antihistamines, diphenhydramine also easily crosses the blood-brain barrier. This means it affects H1 receptors in the central nervous system, leading to its well-known sedative effect. This is why Benadryl is so effective as a sleep aid, but also why it causes significant drowsiness that can interfere with daily activities. Additionally, diphenhydramine has anticholinergic effects, meaning it blocks acetylcholine receptors. This action helps to dry up mucus secretions but can also cause side effects like dry mouth and blurred vision.

A Closer Look at Different Benadryl Formulas

The Benadryl brand encompasses a variety of products, and the specific composition depends on the intended use. It is essential to read the Drug Facts label on any Benadryl product to understand its full ingredient list.

Benadryl Allergy (Oral): The classic formula contains only one active ingredient: diphenhydramine HCl (typically 25mg per dose).
Benadryl Allergy Plus Congestion (Oral): This multi-symptom version contains two active ingredients: the antihistamine diphenhydramine and the decongestant phenylephrine. The added decongestant helps relieve nasal congestion and sinus pressure.
Benadryl Itch Stopping Cream/Gel/Spray (Topical): For topical products, the ingredients are different. For instance, the cream and gel contain diphenhydramine and zinc acetate, which acts as a skin protectant. The cooling gel may use camphor for pain relief instead of diphenhydramine.

Inactive Ingredients in Oral Benadryl

Beyond the active components, oral Benadryl products, such as the Ultratabs, contain several inactive ingredients that help form the tablet and aid in absorption. Examples include:

Carnauba Wax: A glazing agent to provide a smooth coating.
Croscarmellose Sodium: A disintegrant that helps the tablet break down in the stomach.
D&C Red 27 Aluminum Lake and Titanium Dioxide: Coloring agents used to give the tablets their characteristic pink color.
Dibasic Calcium Phosphate: A filler and binder.
Microcrystalline Cellulose: A binder and filler.
Polyethylene Glycol and Polysorbate 80: Used to aid in the tablet's coating and dissolution.

First vs. Second-Generation Antihistamines

Benadryl, as a first-generation antihistamine, is often compared to newer, second-generation alternatives like Claritin and Zyrtec. The differences in their active ingredients lead to distinct effects and side effect profiles. While Benadryl provides fast-acting relief and sedation, second-generation antihistamines offer longer-lasting, non-drowsy relief for many.


Feature	Benadryl (Diphenhydramine)	Claritin (Loratadine)	Zyrtec (Cetirizine)
Generation	First-generation	Second-generation	Second-generation
Primary Active Ingredient	Diphenhydramine HCl	Loratadine	Cetirizine HCl
Sedation Level	High (Drowsy)	Very low (Non-drowsy)	Low (Less drowsy)
Duration of Action	4–6 hours	24 hours	24 hours
Speed of Action	Rapid (30 min)	1–3 hours	1 hour
Additional Uses	Insomnia, motion sickness	None	None
Best For	Short-term allergy relief, sleep aid, motion sickness	All-day allergy relief	All-day allergy relief

Important Considerations and Warnings

Because Benadryl's active ingredient is a first-generation antihistamine, it comes with important precautions and warnings. Drowsiness is a major consideration, and users should not drive or operate machinery until they know how it affects them. Alcohol can also intensify drowsiness.

Not for Children Under 6: Oral Benadryl products are not approved for use in children under 6 for allergy symptoms and should never be used to make a child sleepy due to the risk of paradoxical excitation.
Caution for Older Adults: The elderly are more susceptible to side effects like drowsiness, dizziness, and confusion. Long-term anticholinergic use may be associated with an increased risk of dementia. Newer antihistamines are generally preferred for older adults.
Interactions: Consult a doctor or pharmacist if taking sedatives, tranquilizers, or any other medications, as Benadryl can interact with them.

For a more detailed list of warnings and interactions, refer to authoritative sources such as MedlinePlus or the prescribing information available on the FDA's DailyMed database.

Conclusion

In summary, what's in Benadryl varies significantly by product, but its most recognized active ingredient is the first-generation antihistamine diphenhydramine HCl. This compound works by blocking histamine to alleviate allergy symptoms, but its ability to cross the blood-brain barrier also causes sedation. Always check the specific product label, as formulas can include other ingredients like decongestants or skin protectants. Due to its sedative and anticholinergic effects, it is crucial to use Benadryl with awareness, especially concerning drowsiness and potential risks for children and older adults. Newer, second-generation antihistamines offer non-drowsy alternatives for those needing all-day allergy relief without impaired coordination.

Frequently Asked Questions

No, the active ingredient varies depending on the product's formulation. While most oral Benadryl products contain diphenhydramine, topical products for itching use different active ingredients like zinc, and multi-symptom oral versions can include a decongestant.

Diphenhydramine is a first-generation antihistamine that works by blocking the action of histamine, a natural chemical in the body that causes allergic symptoms. It also crosses the blood-brain barrier, causing drowsiness.

Yes, Benadryl is commonly used for occasional insomnia due to its sedative effects. However, its use should be short-term, and other sleep issues might indicate an underlying medical condition.

Older adults may be more susceptible to the side effects of Benadryl, such as confusion, dizziness, and cognitive impairment. Safer, less sedating alternatives like second-generation antihistamines are often recommended instead.

Common side effects include drowsiness, dry mouth, blurred vision, dizziness, and constipation. Due to the risk of drowsiness, it is crucial to avoid activities like driving after taking it.

In case of an overdose, you should immediately call for emergency medical attention or contact a poison control center. Symptoms can include agitation, rapid heartbeat, hallucinations, seizures, and coma.

Benadryl is a first-generation antihistamine known for causing significant drowsiness and shorter-term relief. Claritin and Zyrtec are second-generation antihistamines that provide longer-lasting, non-drowsy relief for most people, making them better for daytime use.