Doxepin (Silenor)

What it treats

Doxepin is approved by the U.S. Food and Drug Administration for two quite different jobs, and the dose tells you which one it is doing. At the higher doses used to treat depression and anxiety, often 75 to 300 mg, it acts as a full tricyclic antidepressant. At the very low doses sold under the brand Silenor, 3 mg and 6 mg, it is approved specifically for insomnia.

The low-dose approval is narrow and worth being precise about. It is for insomnia characterized by trouble staying asleep, what clinicians call sleep maintenance. Low-dose doxepin helps people stay asleep and reduces early waking. It does less for trouble falling asleep in the first place.

How it works

A tricyclic antidepressant affects several of the brain's chemical messengers and also blocks several receptors. Which of those actions matters depends entirely on the dose.

At the high antidepressant doses, the full range of effects is in play. At the very low 3 to 6 mg sleep doses, almost all of that drops away, and one action remains. Low-dose doxepin blocks histamine, the same drowsiness pathway behind sedating antihistamines, and does little else. That narrow, targeted effect is why the low dose works as a clean sleep medication rather than as an antidepressant.

What to expect

Low-dose doxepin works the same night it is taken. There is no weeks-long wait, because the sedating effect does not depend on the slow brain changes behind antidepressant treatment.

Its strength is helping with the second half of the night. People tend to notice fewer awakenings and less early-morning waking, rather than a dramatic change in how fast they fall asleep. Some daytime grogginess can show up at first, and it often eases as the body settles.

Common side effects

At the low 3 to 6 mg sleep doses, side effects are uncommon, because the dose is so small. When they do occur, they include:

• Some daytime drowsiness or grogginess.
• Nausea, occasionally.

The anticholinergic effects that tricyclic antidepressants are known for, things like dry mouth and constipation, are minimal at these low sleep doses for the same reason: there simply isn't much drug on board. This is the key reason low-dose doxepin is well tolerated. If a side effect is severe, or it isn't improving, that's a conversation to have with the prescriber rather than a reason to stop on your own.

Serious side effects and warnings

Serious problems are uncommon at sleep doses, but a few points are worth knowing.

Doxepin is a tricyclic antidepressant. Unlike antidepressants taken at full doses, the low-dose Silenor label does not carry a boxed warning. Its prescribing information does note, though, that the risk of suicidal thoughts and behaviors seen with antidepressants in people under 25 cannot be fully ruled out at these low doses. Any worsening of mood, agitation, or new thoughts of self-harm is worth prompt contact with the prescriber.

• MAOI antidepressants. Doxepin must not be combined with MAOI antidepressants, and a gap is needed when switching between them.
• Narrow-angle glaucoma. Caution is needed in people with untreated narrow-angle glaucoma, which a prescriber will ask about.
• Severe urinary retention. Caution is also needed in people with severe trouble emptying the bladder.

Sexual side effects

At the low doses used for sleep, sexual side effects are not a typical concern. Tricyclic antidepressants can affect sexual function, but that tends to happen at the much higher doses used to treat depression, not at 3 to 6 mg.

Weight, appetite, and sleep

Low-dose doxepin is essentially weight-neutral, which sets it apart from some other sedating options used for sleep. It is taken at bedtime, where the drowsiness works in your favor and helps with staying asleep.

Starting and dosing basics

This section is general background, not a dosing instruction for any individual. The right dose is a decision for a prescriber.

The FDA-approved low doses for sleep are the 3 mg and 6 mg Silenor tablets. One practical point matters: low-dose doxepin should not be taken within 3 hours of a meal, because food slows its absorption and can increase next-day effects. It is taken at bedtime, and the prescriber sets and adjusts the dose based on how a person responds.

Missed doses and interactions

Low-dose doxepin is taken only when needed at bedtime, so a missed dose is usually just skipped rather than made up. Don't take two doses to make up for one.

A few interactions matter. Doxepin must not be combined with MAOI antidepressants. Alcohol and other sedating drugs add to drowsiness and should be approached with care. Give every prescriber and pharmacist a full list of your medications and supplements, including over-the-counter ones.

Stopping and tapering

One point in low-dose doxepin's favor as a sleep aid is that it is not a controlled substance. It is not habit-forming, there is no meaningful tolerance to the sleep effect, and it does not cause the complex sleep behaviors, such as sleepwalking, seen with z-drugs.

Because of that, low-dose use is generally straightforward to stop. It is still worth doing with a prescriber's input, so the underlying sleep problem can be looked at rather than left unaddressed.

Pregnancy and breastfeeding

This is an area where individual circumstances matter and the decision belongs with a clinician. Poor sleep carries its own burden, and doxepin also passes into breast milk in small amounts. None of that adds up to one answer that fits everyone. Anyone who is pregnant, planning a pregnancy, or breastfeeding should talk it through with their prescriber so the specific risks and benefits can be weighed for their situation.

Cost and generic availability

Generic low-dose doxepin is available and inexpensive. There is also a low-cost generic doxepin liquid and a 10 mg capsule that prescribers sometimes use at small doses, although the 3 mg and 6 mg Silenor tablets are the FDA-approved low doses for sleep. Generic doxepin contains the same active medication as the brand and works the same way.

Common questions

Why is an antidepressant used for sleep? At the very low 3 to 6 mg doses, doxepin works almost purely by blocking histamine, the same drowsiness pathway used by sedating antihistamines. At those doses it acts as a sleep medication rather than as an antidepressant.

Is low-dose doxepin habit-forming? No. It is not a controlled substance, it does not cause dependence, and there is no meaningful tolerance to its sleep effect, so it can be used longer-term.

How is it different from a sleeping pill like a z-drug? Low-dose doxepin is not a controlled substance and does not cause the complex sleep behaviors, such as sleepwalking, that z-drugs can. It is best at helping people stay asleep rather than fall asleep faster.

Why should I avoid taking it close to a meal? Food slows how the body absorbs doxepin, which can leave more of it active the next day. Taking it at least 3 hours after eating helps avoid extra next-day grogginess.

Does low-dose doxepin cause the side effects tricyclics are known for? Usually not. The anticholinergic effects, like dry mouth and constipation, are minimal at 3 to 6 mg because the dose is so small. That is the main reason low-dose doxepin is well tolerated.

Questions to ask your prescriber

• Is doxepin a good fit for my type of insomnia, since it works best for staying asleep?
• How long should I plan to take it?
• How far apart should my dose and my evening meal be?
• Which side effects should I expect, and which ones should I call about?
• If we decide to stop it later, how would we do that?

Sources

This guide draws on current prescribing information and public health references. It is reviewed for clinical accuracy and updated as guidance changes.

• U.S. Food and Drug Administration. Doxepin hydrochloride (Silenor) prescribing information.
• MedlinePlus, U.S. National Library of Medicine. Doxepin.
• National Institute of Mental Health. Mental health medications.