Diphenhydramine 25mg Caps
It is used to ease allergy signs.
Drug Class
Antihistamine, Sedative, Hypnotic, Antitussive, Antiemetic
Pharmacologic Class
First-generation H1-receptor antagonist
Pregnancy Category
Category B
FDA Approved
Jan 1970
DEA Schedule
Not Controlled
Overview
What is this medicine?
Diphenhydramine is an antihistamine that helps relieve allergy symptoms like sneezing, runny nose, and itchy eyes. It can also make you feel sleepy, so it's often used for short-term insomnia. It works by blocking a natural substance in your body called histamine.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. You can take this medication with or without food, but if it causes stomach upset, take it with food.
Storing and Disposing of Your Medication
Store this medication at room temperature, away from light and moisture. Keep it in a dry place, such as a closet or drawer, and avoid storing it in the bathroom. Keep all medications in a safe location, out of the reach of children and pets. When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless instructed to do so. Instead, check with your pharmacist for guidance on proper disposal or participate in a drug take-back program in your area.
Missing a Dose
If you take this medication regularly and miss a dose, take it as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular schedule. Do not take two doses at the same time or take extra doses. If you take this medication as needed, do not take it more frequently than directed by your doctor.
To use this medication correctly, follow your doctor's instructions and read all the information provided. You can take this medication with or without food, but if it causes stomach upset, take it with food.
Storing and Disposing of Your Medication
Store this medication at room temperature, away from light and moisture. Keep it in a dry place, such as a closet or drawer, and avoid storing it in the bathroom. Keep all medications in a safe location, out of the reach of children and pets. When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless instructed to do so. Instead, check with your pharmacist for guidance on proper disposal or participate in a drug take-back program in your area.
Missing a Dose
If you take this medication regularly and miss a dose, take it as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular schedule. Do not take two doses at the same time or take extra doses. If you take this medication as needed, do not take it more frequently than directed by your doctor.
Lifestyle & Tips
- Avoid driving or operating heavy machinery until you know how this medication affects you, as it can cause significant drowsiness.
- Avoid alcohol and other sedatives while taking this medication, as they can increase drowsiness.
- Drink plenty of fluids to help with dry mouth.
- If using for sleep, take about 30 minutes before bedtime.
Available Forms & Alternatives
Available Strengths:
- Diphenhydramine 50mg/ml Inj, 1ml
- Diphenhydramine Hcl 50mg Caps
- Diphenhydramine 50mg Capsules
- Diphenhydramine 12.5mg/5ml Elixir
- Diphenhydramine 25mg Tablets
- Diphenhydramine 25mg/10ml Liquid
- Diphenhydramine 12.5mg/5ml Liquid
- Diphenhydramine 12.5mg/5ml Liquid
- Diphenhydramine 25mg Caps
- Diphenhydramine 25mg Capsules
- Diphenhydramine 50mg/ml Inj, 1ml
- Diphenhydramine 25mg Tablets
- Diphenhydramine 25mg Capsules
Dosing & Administration
Adult Dosing
Standard Dose:
25-50 mg orally every 4-6 hours as needed
Dose Range:
25 - 50 mg
Condition-Specific Dosing:
insomnia:
50 mg orally at bedtime
motion_sickness:
25-50 mg orally 30 minutes before exposure, then every 4-6 hours as needed
Pediatric Dosing
Neonatal:
Not established
Infant:
Not established (generally not recommended for children <2 years for cough/cold)
Child:
6 to <12 years: 12.5-25 mg orally every 4-6 hours as needed (Max 150 mg/day); 12 years and older: 25-50 mg orally every 4-6 hours as needed (Max 300 mg/day)
Adolescent:
12 years and older: 25-50 mg orally every 4-6 hours as needed (Max 300 mg/day)
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment, use with caution
Moderate:
Consider dose reduction or extended dosing interval (e.g., every 6-8 hours)
Severe:
Consider significant dose reduction or extended dosing interval (e.g., every 8-12 hours)
Dialysis:
Not significantly removed by dialysis; administer after dialysis if dose adjustment is needed
Hepatic Impairment:
Mild:
No specific adjustment, use with caution
Moderate:
Consider dose reduction or extended dosing interval
Severe:
Consider significant dose reduction or extended dosing interval
Pharmacology
Mechanism of Action
Diphenhydramine is a first-generation antihistamine that competitively blocks H1 histamine receptors in the periphery and in the central nervous system (CNS). Its anticholinergic properties contribute to its antiemetic, antitussive, and sedative effects. It also has local anesthetic properties.
Pharmacokinetics
Absorption:
Bioavailability:
40-60%
Tmax:
1-4 hours
FoodEffect:
Food may delay the rate of absorption but not the extent.
Distribution:
Vd:
17 L/kg
ProteinBinding:
78-85%
CnssPenetration:
Yes
Elimination:
HalfLife:
2.4-9.3 hours (average 4-8 hours)
Clearance:
Not available (highly variable)
ExcretionRoute:
Renal (primarily as metabolites)
Unchanged:
<1% (in urine)
Pharmacodynamics
OnsetOfAction:
15-60 minutes
PeakEffect:
1-4 hours
DurationOfAction:
4-6 hours
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Severe dizziness or fainting
Changes in balance
Feeling less alert than usual
Other Possible Side Effects
Like all medications, this drug can cause side effects. Although many people do not experience any side effects or only have mild ones, it is essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms that bother you or do not go away, contact your doctor:
Dizziness or drowsiness
Thickening of mucus in the nose or throat
Feeling nervous or excitable
Upset stomach or vomiting
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Severe dizziness or fainting
Changes in balance
Feeling less alert than usual
Other Possible Side Effects
Like all medications, this drug can cause side effects. Although many people do not experience any side effects or only have mild ones, it is essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms that bother you or do not go away, contact your doctor:
Dizziness or drowsiness
Thickening of mucus in the nose or throat
Feeling nervous or excitable
Upset stomach or vomiting
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe drowsiness or dizziness
- Difficulty urinating
- Blurred vision or eye pain
- Fast or irregular heartbeat
- Confusion or hallucinations (especially in elderly)
- Paradoxical excitation (restlessness, nervousness, hyperactivity, especially in children)
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances. Be sure to describe the allergic reaction and its symptoms.
If you are breastfeeding or plan to breastfeed, as you may need to avoid breastfeeding while taking this medication.
If the patient is a premature baby or newborn, as this form of the medication should not be given to them.
This is not an exhaustive list of all potential interactions with this medication. Therefore, it is crucial to discuss the following with your doctor and pharmacist:
All medications you are currently taking, including prescription and over-the-counter drugs, natural products, and vitamins.
* Any health problems you have, as they may interact with this medication.
To ensure your safety, do not start, stop, or change the dose of any medication without first consulting your doctor. It is vital to verify that it is safe to take this medication with all your other medications and health conditions.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances. Be sure to describe the allergic reaction and its symptoms.
If you are breastfeeding or plan to breastfeed, as you may need to avoid breastfeeding while taking this medication.
If the patient is a premature baby or newborn, as this form of the medication should not be given to them.
This is not an exhaustive list of all potential interactions with this medication. Therefore, it is crucial to discuss the following with your doctor and pharmacist:
All medications you are currently taking, including prescription and over-the-counter drugs, natural products, and vitamins.
* Any health problems you have, as they may interact with this medication.
To ensure your safety, do not start, stop, or change the dose of any medication without first consulting your doctor. It is vital to verify that it is safe to take this medication with all your other medications and health conditions.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication.
To minimize the risk of severe side effects, do not exceed the dosage prescribed by your doctor. Taking more than the recommended amount can increase your chance of experiencing serious adverse effects. Additionally, do not take this medication for a longer duration than specified by your doctor.
Until you are aware of how this medication affects you, avoid operating a vehicle or engaging in activities that require alertness.
Do not use this medication in conjunction with other products containing diphenhydramine. It is also recommended to avoid consuming alcohol while taking this drug.
Before using marijuana, other forms of cannabis, or prescription or over-the-counter (OTC) medications that may cause drowsiness, consult with your doctor.
Note that different brands of this medication may be suitable for children of varying ages. Prior to administering this medication to a child, consult with their doctor. Furthermore, do not use this medication as a means to induce sleep in children; instead, discuss alternative solutions with their doctor.
If you are 60 years or older, exercise caution when using this medication, as you may be more susceptible to side effects. Similarly, when administering this medication to a child, use it with caution, as children may have a higher risk of experiencing excitability.
If you are pregnant or planning to become pregnant, inform your doctor, as they will need to discuss the potential benefits and risks of using this medication during pregnancy with you.
To minimize the risk of severe side effects, do not exceed the dosage prescribed by your doctor. Taking more than the recommended amount can increase your chance of experiencing serious adverse effects. Additionally, do not take this medication for a longer duration than specified by your doctor.
Until you are aware of how this medication affects you, avoid operating a vehicle or engaging in activities that require alertness.
Do not use this medication in conjunction with other products containing diphenhydramine. It is also recommended to avoid consuming alcohol while taking this drug.
Before using marijuana, other forms of cannabis, or prescription or over-the-counter (OTC) medications that may cause drowsiness, consult with your doctor.
Note that different brands of this medication may be suitable for children of varying ages. Prior to administering this medication to a child, consult with their doctor. Furthermore, do not use this medication as a means to induce sleep in children; instead, discuss alternative solutions with their doctor.
If you are 60 years or older, exercise caution when using this medication, as you may be more susceptible to side effects. Similarly, when administering this medication to a child, use it with caution, as children may have a higher risk of experiencing excitability.
If you are pregnant or planning to become pregnant, inform your doctor, as they will need to discuss the potential benefits and risks of using this medication during pregnancy with you.
Overdose Information
Overdose Symptoms:
- Severe drowsiness or coma
- Dilated pupils
- Flushed skin
- Dry mouth and eyes
- Urinary retention
- Constipation
- Hallucinations
- Seizures
- Tachycardia
- Arrhythmias
- Respiratory depression
What to Do:
Seek immediate medical attention. Call 911 or Poison Control at 1-800-222-1222. Treatment is supportive and symptomatic, including activated charcoal if appropriate, and benzodiazepines for seizures or severe agitation.
Drug Interactions
Contraindicated Interactions
- Monoamine Oxidase Inhibitors (MAOIs) concurrently or within 14 days of use (risk of anticholinergic crisis)
Major Interactions
- CNS depressants (e.g., alcohol, opioids, benzodiazepines, sedatives, hypnotics, anxiolytics) - additive sedation and respiratory depression
- Anticholinergic agents (e.g., tricyclic antidepressants, atropine, some antipsychotics) - additive anticholinergic effects (dry mouth, urinary retention, constipation, blurred vision, confusion)
Moderate Interactions
- CYP2D6 inhibitors (e.g., fluoxetine, paroxetine, quinidine) - may increase diphenhydramine plasma concentrations
- Potassium chloride (oral) - increased risk of GI lesions due to anticholinergic effects
Minor Interactions
- Acetylcholinesterase inhibitors (e.g., donepezil) - may reduce efficacy of cholinesterase inhibitors
Monitoring
Baseline Monitoring
Symptom assessment (allergies, insomnia, cough)
Rationale: To determine appropriateness of therapy and establish baseline for efficacy.
Timing: Prior to initiation
Medical history (glaucoma, BPH, asthma, cardiovascular disease)
Rationale: To identify contraindications or conditions requiring caution.
Timing: Prior to initiation
Routine Monitoring
Efficacy (symptom relief)
Frequency: As needed, with each dose
Target: Reduction in allergy symptoms, improved sleep, reduced cough/nausea
Action Threshold: Lack of efficacy may indicate need for alternative therapy or dose adjustment (within limits)
Adverse effects (sedation, anticholinergic effects)
Frequency: With each dose, especially initially
Target: Minimal or tolerable side effects
Action Threshold: Excessive sedation, dizziness, dry mouth, blurred vision, urinary retention, or confusion warrants dose reduction or discontinuation.
Symptom Monitoring
- Drowsiness
- Dizziness
- Dry mouth
- Blurred vision
- Urinary retention
- Constipation
- Nausea
- Nervousness
- Paradoxical excitation (especially in children or elderly)
- Confusion (especially in elderly)
Special Patient Groups
Pregnancy
Generally considered low risk (Category B), but use only if clearly needed and potential benefits outweigh risks. Consult a healthcare provider.
Trimester-Specific Risks:
First Trimester:
No clear evidence of increased risk of major birth defects.
Second Trimester:
Generally considered safe for occasional use.
Third Trimester:
Use with caution near term as it may cause irritability or drowsiness in the newborn, and theoretical risk of premature labor due to anticholinergic effects.
Lactation
Excreted into breast milk. Use with caution. May cause drowsiness or irritability in the infant and may decrease milk supply, especially with regular use or high doses. Consider alternative antihistamines with less sedation if possible.
Infant Risk:
Low to moderate (L3). Potential for infant drowsiness, irritability, and decreased milk supply.
Pediatric Use
Not recommended for children under 2 years of age for cough/cold symptoms due to risk of serious side effects including respiratory depression and paradoxical excitation. Use with caution and appropriate dosing in older children. Risk of paradoxical excitation (restlessness, nervousness, hyperactivity) is higher in children.
Geriatric Use
Increased sensitivity to anticholinergic effects (e.g., dry mouth, urinary retention, constipation, blurred vision) and CNS effects (e.g., sedation, dizziness, confusion, falls). Start with lower doses and titrate carefully. Avoid use as a primary sleep aid due to Beers Criteria recommendations.
Clinical Information
Clinical Pearls
- Diphenhydramine is a common ingredient in many OTC cold, allergy, and sleep aid products; advise patients to check labels to avoid accidental overdose or additive sedation.
- Due to its significant sedative and anticholinergic effects, it is generally not preferred for chronic allergy management when less sedating options are available.
- Paradoxical excitation (restlessness, nervousness, hyperactivity) can occur, especially in young children and the elderly, rather than sedation.
- Included in the Beers Criteria as a potentially inappropriate medication for older adults due to its strong anticholinergic properties and high risk of sedation and falls.
Alternative Therapies
- Second-generation antihistamines (e.g., loratadine, cetirizine, fexofenadine) for allergy symptoms (less sedating)
- Nasal corticosteroids (e.g., fluticasone, mometasone) for allergic rhinitis
- Decongestants (e.g., pseudoephedrine, phenylephrine) for nasal congestion
- Non-pharmacological sleep aids (e.g., sleep hygiene, melatonin, cognitive behavioral therapy for insomnia)
- Dextromethorphan (for cough)
Cost & Coverage
Average Cost:
$5 - $20 per 100 capsules (25mg)
Generic Available:
Yes
Insurance Coverage:
Generally not covered by prescription plans as it is an inexpensive OTC medication. May be covered by FSA/HSA.
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it's a good idea to check with your pharmacist for more information. If you have any questions or concerns about this medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide details about the medication, including the amount taken and the time it happened, to facilitate prompt and effective treatment.