Unisom vs Benadryl

Unisom vs Benadryl – detailed comparison:


It is the brand name of a medication called doxylamine, a first-generation antihistamine.


This medication is used as a short-term treatment for insomnia, a condition described by difficulty staying asleep or falling asleep.

Mechanism of Action

It works by reducing the effects of histamine, a neurotransmitter in the body, which produces symptoms such as itching, a runny nose, and watery eyes.

In addition, this antihistamine is used to treat watery eyes, sneezing, a runny nose, skin rash, itching, hives, and other allergy or cold symptoms.

It can be used in adults and children 12 years of age and older.

Note – this medication can increase the risk of falls, hence, seniors shouldn’t use it.


For insomnia, the usual recommended dosage is 25mg per day, taken 30 minutes before bedtime.

If you have trouble sleeping, you should not use this medication for more than 14 days unless recommended by your physician.


Before taking this medication, tell your healthcare provider if you have:

  • problems with urination;
  • glaucoma;
  • emphysema;
  • an enlarged prostate;
  • asthma.

Pregnancy & Breastfeeding

This medication is not expected to be harmful to a developing fetus. Do not use this antihistamine without a healthcare provider’s advice if you are pregnant or plan to fall pregnant.

This medication may pass into breast milk and negatively affect a nursing baby. Do not use this antihistamine without a healthcare provider’s advice if you are breastfeeding an infant.

Side Effects and Precautions

Common side effects may include:

  • constipation;
  • drowsiness;
  • thick lung secretions;
  • mild dizziness;
  • sweating;
  • stomach pain;
  • dry nose, mouth, or throat;
  • blurred vision;
  • headaches;
  • loss of coordination.

Less common side effects may include:

  • severe drowsiness or dizziness;
  • sensitivity to light;
  • toxic psychosis;
  • irregular heart rate;
  • low blood cell counts;
  • erectile dysfunction;
  • abnormal heart rhythms;
  • hyperactivity;
  • severe allergic reaction;
  • seizures;
  • acute labyrinthitis (inner ear problems);
  • low blood pressure;
  • little or no urinating;
  • hallucinations;
  • confusion;
  • difficulty urinating;
  • blurred or double vision.

Drug Interactions

It may negatively interact with other medications, especially:

  • cyclobenzaprine;
  • Cymbalta (duloxetine);
  • Zyrtec (cetirizine);
  • Adderall (amphetamine/dextroamphetamine);
  • Xanax (alprazolam);
  • gabapentin;
  • trazodone;
  • Benadryl (diphenhydramine);
  • tramadol;
  • oxycontin;
  • lisinopril;
  • melatonin;
  • omeprazole;
  • levothyroxine;
  • phendimetrazine;
  • Tylenol (acetaminophen);
  • airborne;
  • ibuprofen.


Consuming alcoholic beverages while using this antihistamine is not recommended since alcohol can increase the risk of side effects.


It is the brand name of a generic drug called diphenhydramine, a potent antihistamine.

Mechanism of Action

It works by blocking the effects of histamine, a natural compound that is released by the body.


This antihistamine is used to treat rashes, hives, itching, a runny nose, sneezing, watery eyes, and other signs and symptoms of seasonal or year-round allergies.

Also, it is used to suppress coughs, to treat motion sickness, to induce sleep, and to treat mild forms of Parkinson’s disease.

Side Effects and Precautions

Common side effects may include:

  • constipation;
  • upset stomach;
  • tiredness;
  • fatigue;
  • enlarged prostate;
  • blurred vision;
  • dizziness;
  • drowsiness;
  • double vision;
  • loss of appetite;
  • nausea;
  • disturbed coordination;
  • dry mouth;
  • headaches;
  • difficulty urinating;
  • tremor.


The recommended dose is 25-50 mg every 4-6 hours. It is not recommended for use in children under 6 years. The maximum recommended dose should not exceed 400 mg per day.


Before using this antihistamine, tell your healthcare professional if you have:

  • an overactive thyroid;
  • glaucoma;
  • blockage in your digestive tract;
  • an allergy to diphenhydramine;
  • kidney disease;
  • a colostomy or ileostomy;
  • an enlarged prostate;
  • a stomach ulcer;
  • chronic obstructive pulmonary disease;
  • liver disease;
  • asthma;
  • increased pressure in the eye;
  • a cough caused by emphysema;
  • bladder obstruction;
  • heart disease;
  • low blood pressure.

Pregnancy & Breastfeeding

It can pass into breast milk and may affect the infant in a negative way, thus, avoid the medication if you are breastfeeding.

There are no clinical studies regarding the safe use of this medication during pregnancy, therefore, contact your doctor before using this antihistamine if you are pregnant or plan to fall pregnant.

Drug Interactions

This antihistamine may interact with:

  • monoamine oxidase inhibitors;
  • over-the-counter cold medicines;
  • any other drugs which make you feel drowsy, sleepy, or relaxed;
  • allergy medicines;
  • antidepressants;
  • anxiety or sleep drugs;
  • potassium supplements, including – Epiklor, Cytra, and Polycitra;
  • prednisolone acetate.


Do not drink alcohol while using this antihistamine since alcohol can increase the risk of side effects, especially drowsiness and dizziness.

Bottom Line – Unisom vs Benadryl      

Unisom (active ingredient – doxylamine) is an antihistamine that can cause drowsiness and is occasionally taken as a sleep aid. This medication is used to treat hives, skin rash, itching, sneezing, runny nose, watery eyes, and other cold or allergy symptoms.

Benadryl (active ingredient – diphenhydramine) is a first-generation antihistamine medicine. This medication is effective in treating symptoms of mild allergy and the common cold as well as sneezing, a runny nose, hives, and itching.

In conclusion, both medications are antihistamines but they contain different active ingredients – Unisom contains doxylamine succinate, whereas Benadryl contains diphenhydramine. You can develop tolerance to diphenhydramine, but not to doxylamine. Both have similar side effects.



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