diphenhydramine
Brand names: Benadryl
Diphenhydramine, also known as Benadryl, is an antihistamine medicine. It helps relieve allergy and cold symptoms.
Drug Pricing (NADAC)
Generic Price
$0.01/unit
Generic Available
Yes (13 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
This medicine temporarily relieves symptoms from allergies or hay fever.
Common side effects
Headache, Fatigue, Nausea
Key warnings
There are no boxed warnings for this medication.
How It Works
Diphenhydramine blocks histamine, a natural substance that your body makes during an allergic reaction. By blocking histamine, it reduces allergy symptoms. It can also dry up nasal passages to relieve a runny nose.
How to Take It
Take this medicine every 4 to 6 hours as needed. Do not take more than 6 doses in 24 hours. Children under 4 years old should not use this medicine. Children 4 to under 6 years old should not use this medicine unless a doctor tells you to. Children 6 to under 12 years old can take 1 to 2 teaspoonfuls (5 ml to 10 ml).
Pregnancy & Breastfeeding
If you are pregnant or breastfeeding, talk to your doctor before using this medicine. It is important to weigh the benefits and risks with your doctor.
Missed Dose
If you miss a dose, take it as soon as you remember. Do not take more than 6 doses in 24 hours.
Storage
Store at room temperature away from moisture and heat.
Side Effects (from patient reports)
Based on 44,288 FDA adverse event reports.
FDA Adverse Event Report Analysis
Detailed analysis of 60,533 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2003–2025.
Total Reports
60,533
Death-Related Reports
11,360
Hospitalization Reports
19,529
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | OFF LABEL USE | 7,772 |
| 2 | HEADACHE | 5,138 |
| 3 | FATIGUE | 5,076 |
| 4 | NAUSEA | 4,484 |
| 5 | PAIN | 4,014 |
| 6 | DRUG INEFFECTIVE | 3,867 |
| 7 | SINUSITIS | 3,668 |
| 8 | TOXICITY TO VARIOUS AGENTS | 3,497 |
| 9 | DYSPNOEA | 3,387 |
| 10 | PYREXIA | 3,386 |
| 11 | INFUSION RELATED REACTION | 3,345 |
| 12 | PNEUMONIA | 3,100 |
| 13 | ARTHRALGIA | 3,001 |
| 14 | INAPPROPRIATE SCHEDULE OF PRODUCT ADMINISTRATION | 2,918 |
| 15 | COMPLETED SUICIDE | 2,811 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
There are no boxed warnings for this medication.
Known Drug Interactions
Anticholinergic Drugs Concomitant treatment with clozapine and other drugs with anticholinergic activity (e.g., benztropine, cyclobenzaprine, diphenhydramine) can increase the risk for anticholinergic toxicity and severe gastrointestinal adverse reactions related to hypomotility.
Mechanism: These two drugs both block certain signals in the body, which can lead to a 'double dose' of side effects like extreme sleepiness and severe constipation. This happens because both medications have similar drying and slowing effects on the body.
What to do: Be careful when using these together and watch for signs of severe constipation or confusion. Consult your healthcare provider before taking over-the-counter allergy or sleep aids while on clozapine.
Diphenhydramine: Diphenhydramine is reported to be a weak inhibitor of aldehyde oxidase in rat liver, but its inhibitory effects in human liver are not known. There is no pharmacokinetic interaction between zaleplon and diphenhydramine following the administration of a single dose (10 mg and 50 mg, respectively) of each drug.
Mechanism: Diphenhydramine might weakly block a liver enzyme, but studies show it does not change how the body processes zaleplon. There is no evidence that these drugs interfere with each other's levels in the blood.
What to do: No dose adjustments are usually needed when taking these two drugs together. Always inform your doctor about all medications you are using.
Common Questions
What is the active ingredient?
Can I give this to my baby?
Will this medicine make me sleepy?
Can I take this with other medicines?
How long does it take to work?
Can I drive after taking this?
What if my symptoms don't improve?
Can I take this for a cough?
Can I drink alcohol while taking this?
How often can I take this?
What are the common side effects of diphenhydramine?
Does diphenhydramine interact with other medications?
What drug class is diphenhydramine?
Is diphenhydramine safe during pregnancy?
Has diphenhydramine been recalled?
Active Recalls
CGMP Deviations; detection of Nitrosamine Drug Substance-Related Impurities (NDSRI), N-nitroso-desmethyl-diphenhydramine (n-dph), above the FDA Recommended Intake Limit
Chattem Inc
CGMP Deviations: Nitrosamine Drug Substance Related Issue impurity above the daily acceptable intake limit defined by the Food and Drug Administration.
Chattem Inc
Labeling: Not Elsewhere Classified: Tablets/Capsules imprinted with wrong ID.
Akron Pharma, Inc.
Labeling: Not Elsewhere Classified: Tablets/Capsules imprinted with wrong ID.
Akron Pharma, Inc.
CGMP Deviations: product held outside appropriate storage temperature conditions.
Family Dollar Stores, Llc.
Lack of Assurance of Sterility: FDA inspection findings resulted in concerns regarding quality control processes
Lowlite Investments, Inc. D/B/A Olympia Pharmacy
Related Medications in First-Generation Antihistamine
Other drugs grouped near diphenhydramine — same-class peers and common alternatives.
azelastine
Astelin, Astepro
Azelastine nasal spray is an antihistamine medicine.
Compare with diphenhydramine →
budesonide nasal
Rhinocort
Rhinocort is a nasal spray that helps relieve allergy symptoms.
Compare with diphenhydramine →
cetirizine
Zyrtec
Cetirizine (Zyrtec) is an antihistamine medicine.
Compare with diphenhydramine →
chlorpheniramine
Chlor-Trimeton
Chlorpheniramine is an antihistamine medicine.
Compare with diphenhydramine →
ciclesonide nasal
Omnaris, Zetonna
Omnaris Nasal Spray is a medicine that helps treat allergy symptoms in your nose.
Compare with diphenhydramine →
Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Pain Relievers Compared
NSAIDs vs acetaminophen — which OTC pain reliever to use
Narrow Therapeutic Index Drugs
Why some drugs demand precise dosing and monitoring
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
Related Health & Safety Data
🩺 Find a Doctor
Search prescribers for First-Generation Antihistamine
🏨 Hospital Quality
CMS hospital ratings, safety scores & patient outcomes
💊 Supplement Data
NIH DSLD — check supplement ingredients & label claims
🍽️ Food Safety Alerts
FDA recalls, inspections & outbreak investigations
⚠️ Product Recalls
FDA, CPSC & NHTSA recall search
💉 Procedure Costs
Medicare procedure pricing for 9,297 procedures
What the FDA Data Shows for diphenhydramine
The FDA label for diphenhydramine (sold under brand names such as Benadryl) classifies it as an over-the-counter product in the First-Generation Antihistamine class. This medicine temporarily relieves symptoms from allergies or hay fever. Official labeling lists 3 commonly reported side effects, including Headache, Fatigue, Nausea.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 44,288 voluntary reports. The database also lists 2 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated moderate severity. NADAC pricing from CMS shows a generic unit cost of $0.01.
Report counts do not establish causation — a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history (currently 6 recall records on file), and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice — always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: January 22, 2025
Read our methodology — how this data is sourced, computed, and verified.
All federal data sources used on this page
- FDA Orange Book — approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed — NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) — post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm — standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files — federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database — current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages