Low-dose doxepin at 3mg or 6mg is FDA-approved for insomnia characterized by difficulty staying asleep, making it one of the few sleep medications in common use that is on-label for the purpose. At those doses it acts as a highly selective histamine H1 antagonist with negligible anticholinergic, adrenergic, and serotonergic activity, which is why it produces little next-day impairment and no dependence. At antidepressant doses of 75mg to 300mg it behaves as a full tricyclic antidepressant with the anticholinergic and cardiac profile of that class. The AASM guideline conditionally recommends it for sleep-maintenance insomnia.
TL;DR: Doxepin is unusual in this category because the low dose holds an approval for insomnia, which most sleep prescriptions do not. At 3mg or 6mg it does a single job: block the histamine that keeps you awake. It works best for the person who falls asleep fine and then wakes at 3am and cannot get back down. It causes very little morning fog, is not addictive, and is not a controlled substance. The catch is that doxepin at 150mg is a different animal altogether, an old antidepressant with dry mouth, constipation, and heart-rhythm concerns. If your bottle says 10mg or higher, you are on the other drug. Sleep apnea should be ruled out before any of this. Tell Dr. Ash how your nights go.
Almost everything prescribed for sleep in America is off-label. Low-dose doxepin is the exception, and that alone makes it worth understanding.
What makes low-dose doxepin different?
The dose changes which receptors it touches, and at the low end it touches almost only one.
Doxepin is a tricyclic antidepressant from the 1960s. Like every tricyclic it binds a long list of receptors: histamine H1, muscarinic acetylcholine, alpha-1 adrenergic, and the serotonin and norepinephrine transporters. Its affinity for those receptors differs by orders of magnitude, and its affinity for H1 is far higher than for any of the others.
At 3mg or 6mg, blood levels are high enough to block H1 substantially and too low to engage the rest meaningfully. What you get is close to a selective antihistamine: sedation, and very little of the dry mouth, constipation, blood-pressure drop, or cardiac conduction effect that defines the tricyclic class.
At 75mg to 300mg, everything else comes online and it behaves as a full tricyclic antidepressant. Same molecule, different drug.
What is it approved for, and what does the evidence say?
Low-dose doxepin holds FDA approval for the treatment of insomnia characterized by difficulty with sleep maintenance, which is the clinical way of saying waking in the night and struggling to get back down.
The American Academy of Sleep Medicine's pharmacologic guideline conditionally recommends doxepin at 3mg to 6mg for sleep-maintenance insomnia. That places it in a small group: the guideline recommends against trazodone, diphenhydramine, melatonin, valerian, and tryptophan, and conditionally for a short list that includes doxepin, eszopiclone, zolpidem, and a few others.
Trials show modest, consistent improvement in wake time after sleep onset and total sleep time, sustained over several weeks, without meaningful next-morning psychomotor impairment and without rebound insomnia or withdrawal on discontinuation. The effect sizes are not dramatic. The safety profile is the selling point.
Who is it best for?
The person whose problem is the second half of the night.
Doxepin's strength is sleep maintenance, and it does relatively little for sleep onset. Somebody who lies awake for two hours at the start of the night is a poor match; somebody who falls asleep in ten minutes and then surfaces at 3am and stares at the ceiling is the target.
It also suits people for whom the usual options are wrong: older adults who should avoid anticholinergics and Z-drugs, people who cannot take controlled substances, and people who have had unacceptable morning grogginess on other agents.
The dose is taken within 30 minutes of bedtime, and not within three hours of a meal, because food substantially raises absorption and can push levels into the range where the other receptors start to matter.
Guidance from the Clinic
What are the side effects?
At 3mg to 6mg, few, and that is the point.
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Reported effects in trials were close to placebo rates for most measures. Somnolence and sedation are the commonest, along with nausea and upper respiratory symptoms. Next-morning psychomotor and memory testing showed little impairment, which distinguishes it from most of the alternatives.
What does not show up at these doses, and does at antidepressant doses, is the reason to keep the dose low: anticholinergic dry mouth, constipation, and urinary retention; orthostatic hypotension; weight gain; and cardiac conduction effects including QT prolongation.
Two cautions remain at any dose. Doxepin should not be combined with a monoamine oxidase inhibitor or taken within 14 days of one. And it is contraindicated in untreated narrow-angle glaucoma and in urinary retention, since even limited anticholinergic activity is unwelcome there.
As with every sedating agent, the sleep apnea question comes first. That is on insomnia or sleep apnea.
Is generic doxepin the same thing?
Chemically yes, practically not always, and the difference is the available strengths.
The branded low-dose product is made in 3mg and 6mg tablets. Generic doxepin has historically been supplied as 10mg, 25mg, 50mg, 75mg, 100mg, and 150mg capsules, plus an oral concentrate. A 10mg capsule is more than three times the low dose and starts to bring the other receptors into play.
The oral solution allows accurate small doses to be measured, which is how some prescribers reach 3mg or 6mg without the branded tablet. Splitting a 10mg capsule is not a reliable way to get there.
The practical instruction: if you have been told you are on low-dose doxepin, check the strength on the bottle. If it says 10mg or more, ask about it.
How does it compare?
Against hydroxyzine and diphenhydramine, doxepin at low dose is the better version of the same idea, since it blocks H1 with far less anticholinergic burden and has FDA approval and a guideline recommendation, neither of which they have. Hydroxyzine for sleep covers that comparison from the other side.
Against trazodone, doxepin has approval and a conditional recommendation where trazodone has a recommendation against it. Trazodone for sleep has the detail.
Against the Z-drugs, doxepin is not a controlled substance, produces no dependence, carries no complex-sleep-behavior warning, and is weaker. That trade favours doxepin for most people and not for everyone. Z-drugs for insomnia covers the other side.
Against CBT-I, it loses on durability, as every drug here does, and it combines with it well.
Key Takeaways
- Low-dose doxepin at 3mg or 6mg is FDA-approved for sleep-maintenance insomnia, which almost nothing else in common use is.
- At that dose it is close to a selective H1 antagonist, so the tricyclic side effects stay absent.
- It targets the second half of the night and does little for falling asleep.
- Check the bottle: a 10mg capsule is more than three times the low dose and is a different drug.
- Do not take it within three hours of a meal, since food raises absorption meaningfully.
Related at Fishtown Medicine
- CBT-I for insomnia
- Hydroxyzine for sleep
- Trazodone for sleep
- Z-drugs for insomnia
- Is it insomnia or sleep apnea?
Scientific References
- US Food and Drug Administration. Silenor (doxepin) tablets prescribing information. FDA Access Data.
- Sateia MJ, Buysse DJ, Krystal AD, Neubauer DN, Heald JL. Clinical Practice Guideline for the Pharmacologic Treatment of Chronic Insomnia in Adults. Journal of Clinical Sleep Medicine. 2017;13(2):307-349.
- Krystal AD, Durrence HH, Scharf M, et al. Efficacy and Safety of Doxepin 1 mg, 3 mg, and 6 mg in Adults with Primary Insomnia. Sleep. 2010;33(11):1553-1561.
- Roth T, Rogowski R, Hull S, et al. Efficacy and safety of doxepin 1 mg, 3 mg, and 6 mg in adults with primary insomnia. Sleep. 2007;30(11):1555-1561.
- Yeung WF, Chung KF, Yung KP, Ng THY. Doxepin for insomnia: a systematic review of randomized placebo-controlled trials. Sleep Medicine Reviews. 2015;19:75-83.
- Stahl SM. Selective histamine H1 antagonism: novel hypnotic and pharmacologic actions challenge classical notions of antihistamines. CNS Spectrums. 2008;13(12):1027-1038.
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