Category- Allopathy
Medicine Highlights
| Uses | 1. To treat Allergies 2. To control Cold symptoms 3. To treat Motion sickness 4. To treat Insomnia |
| Common Side Effects | 1. Dizziness, drowsiness, loss of coordination 2. Dry mouth, nose, or throat 3. Constipation, upset stomach 4. Dry eyes, blurred vision 5. Daytime drowsiness or a “hangover” feeling after night-time use. |
| Additional Information | 1. Avoid driving or any hazardous activity after consuming diphenhydramine, as it can cause dizziness or drowsiness. 2. Its off-label uses include prevention of dystonia, insomnia, pruritus, urticaria, parkinsonism, and vertigo. |
| Storage | 1. The medicine should be stored at room temperature. 2. Keep away from sunlight and moisture. 3. Keep away from the reach of children |
| How to Take This Medicine | Take this medicine orally with a sip of water. |
Diphenhydramine Uses
Diphenhydramine 25 mg is an oral medicine belonging to the category of antihistamines and is used for the following indications:
- Allergies
- Cold symptoms
- Motion sickness
- Insomnia
Diphenhydramine side effects
More Common
- Dizziness, drowsiness, loss of coordination
- Dry mouth, nose, or throat
- Constipation, upset stomach
- Dry eyes, blurred vision
- Daytime drowsiness or a “hangover” feeling after night-time use.
Less Common
- Pounding heartbeats or fluttering in your chest
- Painful or difficult urination
- Little or no urinating
- Confusion, feeling like you might pass out
- Tightness in your neck or jaw, uncontrollable movements of your tongue
How Diphenhydramine works
Diphenhydramine works by blocking histamine H1 receptors; thereby preventing histamine-mediated effects such as sneezing, itching, and swelling. Because it crosses the blood brain barrier, it slows down the normal function of the brain leading to drowsiness and calming effects. Additionally, diphenhydramine has anticholinergic action, which dries secretions and relaxes muscles but can also cause side effects like dry mouth or blurred vision.
Safety Measures and Warning
Pregnancy
The safety of diphenhydramine in pregnancy is not established. Inform your doctor if you are pregnant or planning to conceive.
Breastfeeding
Diphenhydramine is not usually recommended during breastfeeding because there is no reliable information on whether it passes into breast milk or how it might affect a nursing infant.
Kidney and Liver Problems
Diphenhydramine is known to be safe for use in liver and kidney disease patients.
Past Mental Health Issues
Diphenhydramine directly acts on the brain and causes different side effects like sedation, drowsiness, and suicidal thoughts. Inform the doctor about your past mental health issues before using diphenhydramine.
Heart Problems
Diphenhydramine should be used with caution in heart patients, as it can affect influence blood vessel tone and, in rare cases, affect heart rhythm or blood pressure.
Diphenhydramine Interaction with Food Product
Avoid consuming alcohol and smoking simultaneously, as it may affect the drug’s action and show an effect on the brain, leading to severe drowsiness, sedation, and coma in severe cases.
Diphenhydramine Interaction with Other Medicines
Avoid taking Diphenhydramine 25 mg with the following medicines, as it may increase or decrease the desired effect, or in worse cases, it could be fatal:
Diphenhydramine Chemical Structure
IUPAC (International Union of Pure and Applied Chemistry)/ Chemical name
2-(diphenylmethoxy)-N,N-dimethylethanamine
Intake routine/cycle
Daily dose
Take diphenhydramine exactly as your doctor recommends. The dose may change based on your condition and how well you respond. Do not take more than prescribed without consulting your doctor.
Missed Dose
If you forget to take your medicine, take the medication as soon as you remember. If it’s nearly time for your next dose, skip the missed one and continue with your regular schedule. Always consult the doctor before making any changes to your dosage.
Overdose
It is not recommended to take more than 500 mg of Diphenhydramine per day, as it may cause severe overdosing effects like extreme drowsiness, confusion, unconsciousness, sweating, double vision, low blood pressure, and slurred speech. Immediately seek medical attention and meet the doctor if necessary.
Storage
- Store the medicine at room temperature
- Keep away from sunlight and moisture
- Keep out of reach of children
Directions for use
- Take diphenhydramine exactly as prescribed by your doctor, at the same time each day.
- Do not stop taking diphenhydramine without your doctor’s approval, even if you feel better.
- If you forget to take diphenhydramine, take it as soon as you remember. If it’s almost time for your next dose, skip the missed dose.
Diphenhydramine Summary
Diphenhydramine is a common allergy medicine approved for treatment of allergies, cold symptoms, motion sickness, and insomnia. Off label use includes anxiety, and Dystonia (sudden muscle spasm), cough, nausea, Parkinson like stiffness, and comfort care. It works by blocking histamine, the chemical that makes you sneeze, itch, or swell in the body, and also calms the brain, which is why it causes drowsiness. Usual side effects are sleepiness, dry mouth, blurred vision, constipation, and confusion, especially in older adults. Mixing it with alcohol or other sedatives can dangerously increase sleepiness, and grapefruit juice may change how it is absorbed. Children, the elderly, and people with asthma, glaucoma, or prostate problems should avoid this medication, as they may react more strongly to the medicine. Overdose can be serious, typically above 500 to 1000 mg in adults, causing hallucinations, seizures, or heart rhythm problems, so it should always be used carefully and only as directed.
FAQ’s
What are the uses of diphenhydramine tablets?
Diphenhydramine tablets are used to relieve allergy and cold symptoms like sneezing, itching, watery eyes, and runny nose, and help with motion sickness and short-term sleep problems. Doctors may additionally use them for muscle spasms from certain medicines, anxiety, cough, nausea, and comfort care in serious illness.
What are the side effects of diphenhydramine tablets?
Diphenhydramine tablets commonly cause sleepiness, dry mouth, blurred vision, constipation, and dizziness, and in older adults they may lead to confusion, memory problems, or trouble urinating. At higher doses, side effects can include hallucinations, fast heartbeat, or seizures, so the medicine should always be taken carefully and only as directed.
What is diphenhydramine’s highest dose?
The highest safe dose of diphenhydramine for adults is 400 mg in 24 hours, usually taken as 25–50 mg every 4–6 hours. Going beyond this limit can cause dangerous effects like hallucinations, seizures, or heart rhythm problems. Children and older adults have lower limits, so dosing must always follow medical advice.
What is the drug class of diphenhydramine?
Diphenhydramine belongs to the drug class of antihistamines and can show mast cell inhibiting effects.
Reference
- Drugs.com. Diphenhydramine: Uses, Dosage & Side Effects [Internet]. Drugs.com; 2025 [cited 2025 Dec 29]. Available from.
- National Center for Biotechnology Information. Diphenhydramine [Internet]. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2025 [cited 2025 Dec 29]. Available from.
- WebMD. Diphenhydramine Oral: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing [Internet]. WebMD LLC; 2025 [cited 2025 Dec 29]. Available from.
- National Center for Biotechnology Information. PubChem Compound Summary for CID 3100, Diphenhydramine [Internet]. Bethesda (MD): National Library of Medicine; 2025 [cited 2025 Dec 29]. Available from.
Authors
Siva Krishna Adithya Bhumireddy completed Bachelor of Pharmacy from GIET School of Pharmacy affiliated to Andhra University and from his 3rd year of graduation itself he was working as a freelance Medical and Publication writer and having expertise in Systematic reviews and clinical research. With his keen interest and skills in research and documentation practices he also reviewed more than 100 manuscripts from international journals like Elsevier, Springer Nature, Sage Journals and all the manuscripts were indexed and appeared in Pub Med, Scopus and Web of Science databases and received honorary recognition letters and certificates from all of them. Siva Krishna Adithya also published few systematic, narrative reviews and few chapters of international expertise.