Diphenhydramine 25mg Tablets
It is used to ease allergy signs.
Drug Class
Antihistamine, Sedative-Hypnotic, 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 or to help with motion sickness. 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. If it causes stomach upset, taking it with food may help.
Storing and Disposing of Your Medication
Keep your medication at room temperature, away from light and moisture. Avoid storing it in a bathroom. Ensure all medications are kept in a safe location, out of 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, consult your pharmacist for guidance on proper disposal. You may also have access to local drug take-back programs.
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 extra doses. If you take this medication as needed, follow your doctor's instructions and do not take it more frequently than recommended.
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. If it causes stomach upset, taking it with food may help.
Storing and Disposing of Your Medication
Keep your medication at room temperature, away from light and moisture. Avoid storing it in a bathroom. Ensure all medications are kept in a safe location, out of 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, consult your pharmacist for guidance on proper disposal. You may also have access to local drug take-back programs.
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 extra doses. If you take this medication as needed, follow your doctor's instructions and do not take it more frequently than recommended.
Lifestyle & Tips
- Avoid driving or operating heavy machinery until you know how this medicine affects you, as it can cause significant drowsiness.
- Avoid alcohol and other medications that cause drowsiness while taking diphenhydramine.
- To relieve dry mouth, suck on sugar-free candy or ice chips, or use a saliva substitute.
- If using for sleep, take about 30 minutes before bedtime.
- If using for motion sickness, take 30 minutes before travel.
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 mg to 50 mg orally every 4 to 6 hours as needed
Dose Range:
25 - 50 mg
Condition-Specific Dosing:
insomnia:
25 mg to 50 mg orally at bedtime
motion_sickness:
25 mg to 50 mg orally 30 minutes before exposure, then every 4 to 6 hours as needed
allergic_reactions:
25 mg to 50 mg orally every 4 to 6 hours as needed (max 300 mg/day)
Pediatric Dosing
Neonatal:
Not established (contraindicated in premature infants and neonates)
Infant:
Not established (contraindicated in premature infants and neonates)
Child:
6 to <12 years: 12.5 mg to 25 mg orally every 4 to 6 hours as needed (max 150 mg/day); âĨ12 years: 25 mg to 50 mg orally every 4 to 6 hours as needed (max 300 mg/day)
Adolescent:
25 mg to 50 mg orally every 4 to 6 hours as needed (max 300 mg/day)
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment recommended, use with caution due to anticholinergic effects.
Moderate:
Use with caution, consider lower doses or extended dosing intervals.
Severe:
Use with caution, consider lower doses or extended dosing intervals (e.g., 25 mg every 8-12 hours).
Dialysis:
Not significantly dialyzable; use with caution, consider lower doses.
Hepatic Impairment:
Mild:
No specific adjustment recommended.
Moderate:
Use with caution, consider lower doses or extended dosing intervals due to hepatic metabolism.
Severe:
Use with caution, consider lower doses or extended dosing intervals (e.g., 25 mg every 8-12 hours).
Pharmacology
Mechanism of Action
Diphenhydramine is a first-generation antihistamine that competitively blocks histamine H1 receptors in the periphery and central nervous system (CNS). It also possesses significant anticholinergic (muscarinic), antiemetic, and sedative properties due to its action on cholinergic, dopaminergic, and alpha-adrenergic receptors.
Pharmacokinetics
Absorption:
Bioavailability:
40-60%
Tmax:
1-4 hours
FoodEffect:
Food may slightly delay absorption but does not significantly affect bioavailability.
Distribution:
Vd:
17 L/kg (adults)
ProteinBinding:
78-99%
CnssPenetration:
Yes
Elimination:
HalfLife:
2.4-9.3 hours (average 4.3 hours in healthy adults)
Clearance:
Not available
ExcretionRoute:
Primarily renal (as metabolites)
Unchanged:
<1% (renal)
Pharmacodynamics
OnsetOfAction:
15-60 minutes (oral)
PeakEffect:
1-3 hours
DurationOfAction:
4-6 hours
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience 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 or aware
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's 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.
Although rare, this medication can cause severe and potentially life-threatening side effects. If you experience 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 or aware
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's 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
- Severe dry mouth or blurred vision that interferes with daily activities
- Confusion or hallucinations (especially in elderly)
- Paradoxical excitation or restlessness (especially in children)
- Signs of an allergic reaction (rash, hives, swelling of face/lips/tongue, difficulty breathing)
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, always check with your doctor before starting, stopping, or changing the dose of any medication.
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, always check with your doctor before starting, stopping, or changing the dose of any medication.
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, it is recommended that you avoid driving and other activities that require alertness.
You should not use this medication in conjunction with other products containing diphenhydramine. Furthermore, it is advisable to avoid consuming alcohol while taking this drug.
Before using marijuana, other forms of cannabis, or prescription and over-the-counter (OTC) medications that may cause drowsiness, consult with your doctor.
It is crucial to note that different brands of this medication may be suitable for children of varying ages. Therefore, it is essential to consult with your doctor before administering this medication to a child. Moreover, this medication should not be used as a means to induce sleep in children; instead, consult with your doctor for alternative solutions.
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 it is necessary to discuss the potential benefits and risks associated with using this medication during pregnancy.
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, it is recommended that you avoid driving and other activities that require alertness.
You should not use this medication in conjunction with other products containing diphenhydramine. Furthermore, it is advisable to avoid consuming alcohol while taking this drug.
Before using marijuana, other forms of cannabis, or prescription and over-the-counter (OTC) medications that may cause drowsiness, consult with your doctor.
It is crucial to note that different brands of this medication may be suitable for children of varying ages. Therefore, it is essential to consult with your doctor before administering this medication to a child. Moreover, this medication should not be used as a means to induce sleep in children; instead, consult with your doctor for alternative solutions.
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 it is necessary to discuss the potential benefits and risks associated with using this medication during pregnancy.
Overdose Information
Overdose Symptoms:
- Severe drowsiness or deep sleep
- Dilated pupils
- Flushed skin
- Dry mouth and eyes
- Urinary retention
- Constipation
- Hallucinations
- Seizures
- Irregular heartbeat
- Coma
What to Do:
Seek immediate medical attention. Call 911 or Poison Control at 1-800-222-1222. Treatment is supportive and may include activated charcoal, gastric lavage, and management of symptoms.
Drug Interactions
Major Interactions
- Alcohol (increased CNS depression)
- Other CNS depressants (e.g., opioids, benzodiazepines, sedatives, hypnotics, tricyclic antidepressants, anxiolytics) - increased CNS depression
- Anticholinergic drugs (e.g., atropine, scopolamine, tricyclic antidepressants, some antipsychotics) - increased anticholinergic effects (dry mouth, urinary retention, blurred vision, constipation)
Moderate Interactions
- Monoamine Oxidase Inhibitors (MAOIs) - may prolong and intensify anticholinergic effects of diphenhydramine
- Potassium chloride (oral) - increased risk of GI lesions due to slowed GI motility
- Topical anesthetics (e.g., pramoxine) - additive CNS depression if significant systemic absorption
Minor Interactions
- Cholinesterase inhibitors (e.g., donepezil) - may antagonize effects of cholinesterase inhibitors
- Betahistine - theoretical antagonism of histamine effects
Monitoring
Symptom Monitoring
- Sedation/drowsiness
- Dizziness
- Dry mouth
- Blurred vision
- Urinary retention
- Constipation
- Paradoxical excitation (especially in children)
- Allergic reaction symptoms (rash, itching, swelling, severe dizziness, trouble breathing)
Special Patient Groups
Pregnancy
Generally considered safe for occasional use during pregnancy (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 teratogenicity from human studies.
Second Trimester:
Generally considered safe for occasional use.
Third Trimester:
Generally considered safe for occasional use, but caution advised near term as it may cause irritability or drowsiness in the neonate.
Lactation
Excreted into breast milk. May cause drowsiness, irritability, or anticholinergic effects (e.g., dry mouth, decreased milk supply) in the infant. Use with caution, especially in preterm or jaundiced infants. Consider alternative non-sedating antihistamines if possible.
Infant Risk:
Low to Moderate (L3)
Pediatric Use
Contraindicated in premature infants and neonates due to increased risk of adverse effects, including respiratory depression. Use with caution in young children due to potential for paradoxical excitation (restlessness, nervousness, insomnia). Dosing must be weight-based and accurate. Avoid use as a sedative in children under 2 years unless specifically directed by a physician.
Geriatric Use
High risk of adverse effects in the elderly due to increased sensitivity to anticholinergic effects (e.g., confusion, delirium, urinary retention, constipation, falls) and sedation. Included on the Beers List as a medication to avoid in older adults. Use lowest effective dose and with extreme caution, or consider alternative agents.
Clinical Information
Clinical Pearls
- Diphenhydramine is a highly sedating antihistamine; warn patients about impaired driving and operating machinery.
- Its anticholinergic effects can be problematic, especially in the elderly (risk of confusion, urinary retention, constipation) and in patients with glaucoma or prostatic hypertrophy.
- Tolerance to the sedative effect can develop with chronic use for insomnia.
- Paradoxical excitation (restlessness, agitation) can occur, particularly in young children.
- Often used off-label for acute dystonic reactions caused by antipsychotics due to its anticholinergic properties.
Alternative Therapies
- For allergies: Second-generation antihistamines (e.g., loratadine, cetirizine, fexofenadine) - less sedating, fewer anticholinergic effects.
- For insomnia: Melatonin, doxylamine, zolpidem, eszopiclone (prescription hypnotics).
- For motion sickness: Meclizine (less sedating than diphenhydramine), scopolamine patch.
- For cough: Dextromethorphan, guaifenesin.
Cost & Coverage
Average Cost:
$5 - $20 per 30 tablets (25mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe and effective treatment, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it is a good idea to check with your pharmacist for more information. If you have any questions or concerns about your medication, do not hesitate to discuss them with 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 detailed information about the overdose, including the medication taken, the amount, and the time it occurred.