CVS Allergy Relief and Benadryl contain the exact same active ingredient at the exact same strength: diphenhydramine hydrochloride, 25 mg per tablet. They work the same way, kick in at the same speed, and last the same amount of time. The only differences are the label, the price, and minor variations in inactive ingredients like dyes and fillers.
Same Drug, Same Dose
Both products are film-coated tablets containing 25 mg of diphenhydramine hydrochloride, as listed in the FDA’s DailyMed database. Diphenhydramine is a first-generation antihistamine that blocks histamine, the chemical your body releases during an allergic reaction. It’s the compound responsible for relieving sneezing, runny nose, itchy eyes, and hives in both products.
CVS Allergy Relief is what’s known as a store-brand generic. The FDA requires generics to be “bioequivalent” to the brand-name drug, meaning the active ingredient must reach your bloodstream at the same rate and in the same amount. Specifically, the key absorption measures must fall within 80% to 125% of the brand-name product. In practice, most approved generics land much closer to 100%. So when you take one CVS Allergy Relief tablet, your body processes it the same way it would a Benadryl Allergy Ultratab.
How Both Products Work in Your Body
Diphenhydramine is rapidly absorbed after you swallow it. You can expect to start feeling effects within 15 to 30 minutes, with the drug reaching peak levels in your blood about 2 hours after taking it. Relief typically lasts 4 to 6 hours per dose. The drug’s half-life (the time it takes your body to clear half of it) ranges from about 3.4 to 9.2 hours in adults, which is why drowsiness can linger even after the allergy relief fades.
That drowsiness isn’t a side effect unique to either brand. It’s built into how diphenhydramine works. The same mechanism that blocks histamine in your nose also crosses into your brain, which is why this drug doubles as the active ingredient in many over-the-counter sleep aids.
Where They Differ: Inactive Ingredients
The active ingredient is identical, but the inactive ingredients (binders, coatings, dyes) can vary between manufacturers. These substances don’t affect how the drug works, but they matter if you have a sensitivity or allergy to a specific dye or filler. If that applies to you, compare the “inactive ingredients” lists on the back of each box. For most people, these differences are irrelevant.
Price Difference
The main reason to choose one over the other is cost. Brand-name Benadryl Allergy Ultratabs run roughly $0.21 per tablet at retail without insurance. CVS Allergy Relief, like most store-brand generics, is typically priced lower per tablet. Over time, especially if you use diphenhydramine regularly for seasonal allergies or occasional sleep support, the savings from choosing the generic add up. You’re paying extra for the Benadryl name, not for a different medication.
Safety Considerations for Both
Because CVS Allergy Relief and Benadryl deliver the same drug, they carry the same side effects and risks. Common ones include drowsiness, dry mouth, and dizziness. You should avoid driving or operating machinery until you know how diphenhydramine affects you.
Older adults face additional concerns. The American Geriatrics Society lists diphenhydramine on its Beers Criteria, a widely used guide for medications that pose higher risks in people over 65. The body clears diphenhydramine more slowly with age, and its anticholinergic properties (the effects that cause dry mouth and constipation) can accumulate. Repeated use in older adults is associated with increased risk of falls, confusion, delirium, and even dementia with long-term cumulative exposure. This applies equally to both the CVS and Benadryl versions. For older adults who need regular allergy relief, newer antihistamines like cetirizine or loratadine are generally preferred because they don’t cause the same level of sedation or cognitive effects.
For younger, healthy adults using it occasionally, diphenhydramine remains an effective short-term option for allergies or itching. Just keep in mind that it lasts only 4 to 6 hours per dose and causes more drowsiness than second-generation antihistamines.
Which One to Buy
If your goal is allergy relief from diphenhydramine, the CVS store brand does the same job for less money. There is no clinical advantage to choosing Benadryl over the generic. The FDA holds both to the same manufacturing and bioequivalence standards. Pick whichever is cheaper or more convenient, and check the inactive ingredients list only if you have known sensitivities to specific additives.