Benadryl is a common over-the-counter allergy medication that contains the active ingredient diphenhydramine. The concentration of diphenhydramine varies between different formulations of Benadryl. Typically, liquid Benadryl contains 12.5 mg of diphenhydramine per 5 mL (teaspoon) while capsules contain 25 mg per capsule. So to directly answer the question “How many mg of Benadryl per mL?”, the concentration is typically 2.5 mg per mL for liquid formulations.
Common Benadryl Formulations and Dosing
Here is an overview of some of the most common Benadryl products and their dosing:
- Benadryl Allergy Liquid (Cherry Flavored): 12.5 mg diphenhydramine per 5 mL (teaspoon)
- Benadryl Allergy Liquid (Grape Flavored): 12.5 mg diphenhydramine per 5 mL (teaspoon)
- Benadryl Allergy Ultratabs Tablets: 25 mg diphenhydramine per tablet
- Benadryl Allergy Dye-Free LiquiGels: 25 mg diphenhydramine per capsule
- Benadryl One a Day Allergy Relief Tablets: 10 mg diphenhydramine per tablet
The standard adult dose is 25-50 mg of diphenhydramine taken every 4-6 hours as needed. For the liquid forms, this would equal taking 5-10 mL (1-2 teaspoons) every 4-6 hours as needed. Always be sure to carefully read and follow dosing instructions on the specific package you are using.
Converting Between Formulations
Since the concentration of diphenhydramine varies between different Benadryl products, you need to perform conversions to determine equivalent doses between forms:
- 1 teaspoon (5 mL) of liquid Benadryl contains 12.5 mg diphenhydramine
- 1 capsule (1 pill) of Benadryl Ultratabs contains 25 mg diphenhydramine
So for example:
- To get a 25 mg dose from liquid Benadryl, you would need to take 2 teaspoons (10 mL)
- To get a 12.5 mg dose from capsules, you would need to take half of one capsule (0.5 pills)
How Diphenhydramine Works
Diphenhydramine is an antihistamine that blocks the effects of histamine in the body. Histamine is a chemical released by the immune system during an allergic reaction. It causes many of the bothersome symptoms associated with allergies like itchy/watery eyes, sneezing, runny nose, and skin irritation.
By blocking histamine receptors, diphenhydramine provides relief from these allergy symptoms. It also has mild sedative effects, which is why it is commonly used as a sleep aid as well.
Mechanism of Action
More specifically, diphenhydramine is a first-generation H1 antihistamine. It works by binding to and blocking H1 histamine receptors in the body. This prevents histamine from binding to the receptor sites and activating an allergic response.
Additionally, diphenhydramine crosses the blood-brain barrier and affects histamine receptors in the brain, leading to sedation. This can help provide relief from allergy symptoms like runny nose and watery eyes as well as promote drowsiness.
Onset and Duration
Diphenhydramine starts working within 15-30 minutes after it is taken. It reaches peak effectiveness at around 1-2 hours. The effects last for 4-6 hours typically.
When diphenhydramine is being used for sleep, the drowsy effects start within 30-60 minutes and generally last for 6-8 hours but can be highly variable between different people.
Benadryl Dosage Chart
Here is a general Benadryl dosage chart based on age and formulation:
| Age | Liquid (mg/dose) | Chewables (mg/dose) | Capsules/Tablets (mg/dose) |
|---|---|---|---|
| Adults & Children 12+ years | 12.5-25 mg every 4-6 hours | 25-50 mg every 4-6 hours | 25-50 mg every 4-6 hours |
| Children 6-11 years | 6.25 mg every 4-6 hours | 12.5-25 mg every 4-6 hours | 12.5-25 mg every 4-6 hours |
| Children 2-5 years | 5 mg every 4-6 hours | 6.25-12.5 mg every 4-6 hours | 6.25-12.5 mg every 4-6 hours |
Do not give Benadryl to children under 2 years old without medical supervision.
Maximum Daily Dose
The maximum daily dose of diphenhydramine is:
- Adults: 400 mg per day
- Children 12-17 years: 300 mg per day
- Children 6-11 years: 150 mg per day
- Children 2-5 years: 75 mg per day
Benadryl for Dogs
In addition to human use, Benadryl is also commonly used in dogs for treating allergies and travel anxiety. The standard Benadryl dosage for dogs is 1 mg per pound of body weight, given 2-3 times a day. So a 25-pound dog would get 25 mg divided into 2-3 doses daily.
It’s always best to consult your veterinarian before giving Benadryl to your pet since dosing can vary based on factors like the specific health issue being treated.
Benadryl Dosage Chart for Dogs
| Dog’s Weight | Benadryl Dose (2-3 times daily) |
|---|---|
| 10 pounds | 10 mg |
| 15 pounds | 15 mg |
| 25 pounds | 25 mg |
| 50 pounds | 50 mg |
| 75 pounds | 75 mg |
| 100 pounds | 100 mg |
Side Effects of Benadryl
Some potential side effects of Benadryl include:
- Drowsiness
- Dizziness
- Headache
- Dry mouth
- Nausea
- Fatigue
- Appetite changes
- Constipation
- Urinary retention
- Vision changes
- Confusion (more common in elderly patients)
Due to its sedative effects, it’s recommended to use caution when driving or operating machinery after taking Benadryl. It’s also important to avoid alcohol while using Benadryl.
Severe Reactions
Call your doctor right away if you experience signs of a serious allergic reaction after using Benadryl such as:
- Rash
- Itching
- Hives
- Swelling of the face, lips, tongue, or throat
- Wheezing or difficulty breathing
Drug Interactions
The following drugs can potentially interact with Benadryl:
- Alcohol – increases drowsiness
- Opioids like codeine – dangerous sedation effects
- Sleeping pills
- Anti-depressants like SSRIs and MAOIs
- Anti-nausea drugs
- Muscle relaxants
- Seizure medications
- Urinary antispasmodics
Always let your doctor know about any other medications you are taking before starting Benadryl. Your doctor may advise avoiding use of these other drugs within ~2-4 hours of your scheduled Benadryl dose to reduce interaction risk.
Who Should Not Take Benadryl?
The following groups should generally avoid using Benadryl:
- Children under age 2 (unless advised by a doctor)
- Adults over age 65 – increased sensitivity, higher chance of confusion/falls
- Pregnant women – should be used only if clearly needed
- Nursing mothers – small amounts enter breast milk and can cause drowsiness in infant
- People with glaucoma
- People with enlarged prostate or urination problems
- People with a breathing disorder like COPD or asthma
- People with liver disease
Talk to your doctor before using Benadryl if you have any medical conditions or take other medications. Your doctor can help determine if it is safe for you to use.
Overdose Symptoms
Taking too much Benadryl can be very dangerous. Symptoms of overdose include:
- Extreme drowsiness
- Dilated pupils
- Rapid heart rate
- Confusion and hallucinations
- Dizziness
- Trouble breathing
- Trembling
- Weakness
- Loss of consciousness
- Seizures
- Coma
Seeking immediate medical help is vital for a Benadryl overdose. Call 911 if you or someone you know may have overdosed.
Treatment
Treatment depends on the severity of the overdose but may include:
- Activated charcoal to prevent absorption
- Gastric lavage to flush out the stomach contents
- IV fluids and respiratory support if needed
- Heart monitoring
- Medications to treat agitation, seizures, widened blood vessels, etc.
Abuse Potential
Although uncommon, Benadryl does carry some risk of abuse due to its sedative effects. Teenagers or people with a history of substance abuse may take high doses of Benadryl to try to get high. However, this is extremely dangerous and can result in overdose.
Signs of Benadryl abuse include:
- Taking more than the recommended dosage
- Continuing to use despite harmful effects
- Combining with alcohol or other drugs
- Obsessive use or inability to stop using
- Hiding use from others
- Using old or expired Benadryl found around the house
Benadryl abuse can harm the brain, heart, digestive system, and other body systems. If you suspect someone is abusing Benadryl, seek help from their doctor right away.
Dependence
It is possible to become dependent on the drowsy effects of diphenhydramine after regular use over an extended period. This can make it difficult to sleep without Benadryl. However, true addiction is very rare.
To reduce dependence, doctors recommend only using Benadryl intermittently as needed for allergies rather than every day. Slowly tapering off over time under medical supervision can also help if dependence occurs.
Conclusion
In summary, liquid Benadryl typically contains 12.5 mg of the active ingredient diphenhydramine per teaspoon (5 mL). The maximum daily dose for adults and children over age 12 is 400 mg. When used as directed, Benadryl is a generally safe and effective medication for relieving allergy symptoms. However, misuse can lead to serious side effects. Always follow dosage recommendations carefully and talk to your doctor if you have any concerns.