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Generic Name: doxylamine
Brand Names: Unisom
Drug Class: Sedative/Hypnotics; Antihistamines, Ethanolamine Derivatives
What is doxylamine, and what is it used for?
Doxylamine is an over-the-counter sedative medication used as a sleep aid by people suffering from insomnia. Doxylamine is a sedative/hypnotic and is also an antihistamine drug that is used to relieve symptoms of upper respiratory tract allergies such as allergic rhinitis, hay fever and common cold, and nausea and vomiting associated with pregnancy. Doxylamine is a first-generation antihistamine that can easily cross the blood-brain barrier and induce drowsiness, unlike the second-generation antihistamines.
Doxylamine blocks the activity of histamine, a natural compound in the body, by binding to H1 histamine receptors, the protein molecules on cell surfaces that respond to histamine. Doxylamine binds non-selectively to all H1 receptors, including in the central and peripheral nervous systems, uterus, gastrointestinal tract, large blood vessels, and bronchial muscles.
Doxylamine works in the following ways:
- Blocks H1 histamine receptors in the sleep center in the brain causing drowsiness
- Reduces nausea and vomiting by inhibiting histaminergic signaling from the chemoreceptor trigger zone to the vomiting center in the medulla region of the brain
- Inhibits histamine receptors in the bronchial muscles, relieving upper respiratory tract allergy symptoms
- Suppresses the function of labyrinth, the middle ear chamber that helps maintain balance and hence causes the side effects of loss of balance and vertigo
Warnings
- Do not use in patients who are hypersensitive to doxylamine or any of its components
- Do not use to treat insomnia in children below 12 years of age; may cause paradoxical excitation in young children
- Do not use doxylamine for longer than two weeks; consult your physician
- May cause central nervous system depression (CNS) impairing physical and mental abilities required for activities such as driving and operating heavy machinery
- Use chlorpheniramine with caution if you have any of the following conditions:
- Narrow angle glaucoma and elevated intraocular pressure
- Prostatic hypertrophy
- Pyloroduodenal obstruction
- Bladder neck obstruction
- Asthma or other respiratory disease
- Cardiovascular disease
- Thyroid dysfunction
- Avoid concurrent use with monoamine oxidase inhibitors (MOAIs)
- Avoid use with other central nervous system (CNS) depressants including alcohol; may potentiate CNS effects
What are the side effects of doxylamine?
Side effects of doxylamine may include:
- Rapid heartbeat (tachycardia)
- Palpitations
- Upper abdominal pain (epigastric pain)
- Diarrhea
- Constipation
- Loss of appetite (anorexia)
- Dry mouth (xerostomia)
- Dryness of mucous membranes
- Painful urination (dysuria)
- Urinary retention
- Headache
- Disorientation
- Drowsiness
- Dizziness
- Vertigo
- Paradoxical central nervous system (CNS) stimulation
- Blurred vision
- Double vision (diplopia)
This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug.
Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.
QUESTION
What is insomnia?
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What are the dosages of doxylamine?
Tablets
- 25 mg
Adults and Children over 12 years old:
- 25 mg orally every evening as needed 30 minutes before bedtime
- Not recommended for use in children under 12 years old
Adults
Upper respiratory tract allergy
- 50 mg orally every 4-6 hours
Geriatric
- Avoid use in the elderly because of the high incidence of anticholinergic effects
- Clearance is reduced with advanced age, greater risk of confusion, dry mouth, constipation, and other anticholinergic effects and toxicity
- May exacerbate existing lower urinary conditions or benign prostatic hyperplasia
- Tolerance develops when used as hypnotic
What drugs interact with doxylamine?
Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.
- Doxylamine has no known severe interactions with other drugs.
- Serious interactions of doxylamine include:
- benzhydrocodone/acetaminophen
- calcium/magnesium/potassium/sodium oxybate
- fentanyl (including intranasal, transdermal and transmucosal)
- hydrocodone
- isocarboxazid
- lemborexant
- methylene blue
- metoclopramide intranasal
- selinexor
- valerian
- Doxylamine has moderate interactions with at least 167 different drugs.
- Mild interactions of doxylamine include:
- ashwagandha
- brimonidine
- eucalyptus
- nettle
- sage
- Siberian ginseng
The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.
It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.
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Pregnancy and breastfeeding
- Doxylamine use is acceptable during pregnancy. Doxylamine can be used to treat nausea and vomiting of pregnancy.
- It is not known if doxylamine is present in breast milk, but is likely present because many drugs are; use with caution and monitor breastfed infants for irritability and drowsiness.
What else should I know about doxylamine?
- Take doxylamine exactly as per the instructions on the label; seek medical help immediately in case of overdose
- Do not use regularly for longer than 2 weeks
- Store doxylamine out of reach of children
- Doxylamine may affect mental alertness and physical ability; do not engage in activities such as driving or operating heavy machinery after taking doxylamine
- Do not drink alcohol or take alcohol-containing drugs while on doxylamine therapy
