From the Guidelines
Yes, doxylamine is an antihistamine, specifically a first-generation antihistamine that blocks H1 histamine receptors in the body. Doxylamine is commonly found in over-the-counter sleep aids (typically at 25 mg doses) and in combination cold/flu products (usually at 12.5 mg doses) 1. It works by preventing histamine from binding to H1 receptors, which helps reduce allergy symptoms, but its main therapeutic use is for short-term treatment of insomnia and as part of cold/flu symptom relief. As a first-generation antihistamine, doxylamine readily crosses the blood-brain barrier, which explains its sedating effects 1. This sedation is why it's effective as a sleep aid but also why it causes drowsiness as a side effect. Other common side effects include dry mouth, blurred vision, urinary retention, and constipation due to its anticholinergic properties. Unlike newer second-generation antihistamines like loratadine or cetirizine, doxylamine is not typically used as a primary treatment for allergies because of these sedating effects.
Some key points to consider when using doxylamine include:
- Its sedating effects can be beneficial for short-term treatment of insomnia, but may cause drowsiness and impaired performance during the day 1
- Doxylamine can cause anticholinergic side effects, such as dry mouth, blurred vision, and constipation 1
- It is not typically used as a primary treatment for allergies due to its sedating effects, but may be used in combination with other medications for cold/flu symptom relief 1
- Doxylamine can interact with other medications, such as sedatives and antidepressants, and may worsen performance impairment and increase the risk of accidents 1
Overall, doxylamine should be used with caution and only as directed, due to its potential for sedating effects and anticholinergic side effects. Patients should be advised to avoid driving or operating heavy machinery while taking doxylamine, and to be aware of the potential for interactions with other medications 1.
From the Research
Doxylamine Classification
- Doxylamine is classified as an anti-H1 hypnotic 2
- It is used to treat insomnia, specifically occasional insomnia in adults 2
- Doxylamine has been compared to other medications, such as doxepin, in terms of its effectiveness in treating insomnia 2, 3
Mechanism of Action
- Doxylamine acts as a histamine H1 inverse agonist 2
- This mechanism of action contributes to its effectiveness in treating insomnia 2