Doxepin (Silenor)

FDA Approved

Tricyclic Antihistamine | Ultra-Low Dose Sleep Aid

Weight: 279.38 Da

Half-life: ~15 hours

4 studies

2011 latest

FDA Approved

Dose 3-6 mg at bedtime (sleep)

Frequency Once daily at bedtime

Cycle As prescribed, often ongoing

Storage Room temperature (68-77F). Protect from moisture and light.

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Doxepin is a tricyclic compound with a remarkably dose-dependent pharmacological profile. At higher doses (75-300 mg), it functions as a traditional tricyclic antidepressant (TCA) with activity across multiple neurotransmitter systems. However, at ultra-low doses (3-6 mg), doxepin acts almost exclusively as a highly selective histamine H1 receptor antagonist, making it one of the most targeted sleep maintenance agents available. This ultra-low dose formulation was approved by the FDA in 2010 under the brand name Silenor specifically for the treatment of insomnia characterized by difficulty with sleep maintenance. The distinction between high-dose and ultra-low dose doxepin is critical: at 3-6 mg, the drug avoids the anticholinergic, noradrenergic, and serotonergic side effects that characterize tricyclic antidepressants, resulting in a remarkably clean side effect profile. For biohackers and those seeking a non-habit-forming sleep aid, ultra-low dose doxepin offers a compelling option -- it does not produce dependence, does not cause rebound insomnia upon discontinuation, and maintains efficacy with long-term use. Unlike benzodiazepines and Z-drugs, it carries no abuse potential and is not a scheduled substance.

Mechanism of Action

At ultra-low doses (3-6 mg), doxepin's mechanism of action is dominated by potent and selective antagonism of the histamine H1 receptor. Doxepin has one of the highest affinities for the H1 receptor of any known compound (Ki approximately 0.17 nM), which means that even at very low plasma concentrations, it effectively blocks histaminergic wakefulness signaling. The histamine system is a key component of the ascending arousal pathway -- histaminergic neurons in the tuberomammillary nucleus of the hypothalamus fire during wakefulness and become quiescent during sleep. By blocking H1 receptors, ultra-low dose doxepin reduces this wake-promoting signal, particularly during the latter half of the night when endogenous histamine levels naturally begin to rise, which is why it is especially effective for sleep maintenance insomnia. At these low doses, doxepin has negligible affinity for muscarinic, adrenergic, and serotonergic receptors, which explains the absence of anticholinergic side effects (dry mouth, constipation, urinary retention) and cardiovascular effects that plague higher-dose TCA use. At antidepressant doses (75-300 mg), doxepin additionally inhibits reuptake of serotonin and norepinephrine and blocks muscarinic, alpha-1 adrenergic, and 5-HT2 receptors, producing a much broader and less selective pharmacological profile.

01 FDA-approved specifically for sleep maintenance insomnia at ultra-low doses (3-6 mg as Silenor)

02 Highly selective H1 antihistamine at low doses, avoiding the side effects of traditional tricyclic antidepressants

03 Non-habit-forming with no dependence, tolerance, or abuse potential

04 No rebound insomnia upon discontinuation, unlike benzodiazepines and Z-drugs

05 Particularly effective for maintaining sleep in the latter half of the night, when many other sleep aids have worn off

06 Extremely well-tolerated side effect profile at ultra-low doses

Molecular Data

Molecular Weight

279.38 Da

Type

Tricyclic dibenzoxepin derivative (C19H21NO)

Peak 0.0 mcg

Trough 0.0 mcg

SS Peak 0.0 mcg

SS Trough 0.0 mcg

Research Indications

FDA-Approved

Insomnia (Sleep Maintenance) most effective

Silenor (doxepin 3 mg and 6 mg) is FDA-approved for the treatment of insomnia characterized by difficulty with sleep maintenance. Clinical trials demonstrated that ultra-low dose doxepin significantly improved sleep maintenance (wake after sleep onset) and total sleep time without next-morning residual effects at the 3 mg dose, and with minimal residual effects at 6 mg.

Major Depressive Disorder effective

At higher doses (75-300 mg), doxepin is FDA-approved for the treatment of depression and anxiety associated with depression. However, this use is largely historical, as newer antidepressants with more favorable side effect profiles have supplanted TCAs for most patients. The antidepressant dosing range is entirely separate from the ultra-low dose sleep application.

Off-Label

Chronic Insomnia (Long-Term Use) effective

Clinical data supports the efficacy and safety of ultra-low dose doxepin for long-term insomnia management. Unlike many hypnotics, doxepin at 3-6 mg maintains its efficacy over months of continuous use without dose escalation, making it suitable for chronic insomnia in patients who need a sustainable, long-term solution.

Insomnia in Older Adults effective

Ultra-low dose doxepin is one of the few sleep medications with specific safety and efficacy data in elderly patients. The 3 mg dose is recommended for older adults and has been shown to improve sleep maintenance without the falls, cognitive impairment, and next-day sedation risks associated with benzodiazepines and Z-drugs in this population.

Dosing Protocols

Ultra-low dose doxepin is available as Silenor tablets (3 mg, 6 mg). Higher-dose formulations for depression are available as generic capsules (10 mg, 25 mg, 50 mg, 75 mg, 100 mg, 150 mg) and an oral concentrate. For sleep, only the 3 mg and 6 mg tablets are appropriate. The drug should be taken within 30 minutes of bedtime and not within 3 hours of a meal, as food can delay absorption and increase the risk of next-day drowsiness.

Goal	Dose	Frequency	Route
Sleep Maintenance - Starting Dose	3 mg	Once at bedtime	Oral tablet
Sleep Maintenance - Standard Dose	6 mg	Once at bedtime	Oral tablet

Interactions

Trazodone

Both doxepin and trazodone promote sleep through different mechanisms. Combining them can result in excessive sedation, prolonged next-day drowsiness, and additive CNS depression. Stacking multiple sleep aids is generally unnecessary and increases the risk of adverse effects. If transitioning between the two, allow adequate washout time.

monitor

SSRIs (e.g., Sertraline, Fluoxetine)

SSRIs can inhibit the CYP2D6-mediated metabolism of doxepin, potentially increasing plasma levels. At ultra-low doses (3-6 mg), this interaction is unlikely to be clinically significant, but monitoring for increased sedation is prudent. At higher antidepressant doses, the interaction is more relevant and serotonin syndrome risk increases.

monitor

MAOIs

Concurrent use of doxepin with monoamine oxidase inhibitors is contraindicated. The combination can precipitate serotonin syndrome, hypertensive crisis, and severe adverse reactions. Allow a minimum 14-day washout period between discontinuing an MAOI and starting doxepin, and vice versa.

avoid

Alcohol

Alcohol potentiates the sedative and CNS-depressant effects of doxepin, even at ultra-low doses. The combination increases the risk of excessive drowsiness, impaired coordination, and next-day cognitive impairment. Alcohol should be avoided on evenings when doxepin is taken.

avoid

What to Expect

30-60 minutes

Onset of drowsiness. Doxepin is absorbed relatively quickly, and most users begin to feel sleepy within 30-60 minutes. Taking the dose on an empty stomach (no food within 3 hours) ensures optimal absorption timing.

2-3 hours

Peak plasma concentration reached. Maximum sedative effect is felt. At ultra-low doses, the sedation is subtle and natural-feeling -- more like a gentle quieting of wakefulness than forced unconsciousness.

4-8 hours

Sustained sleep maintenance. Due to its long half-life (~15 hours) and potent H1 affinity, doxepin continues to block histamine-driven wakefulness throughout the night. This is where doxepin excels compared to shorter-acting sleep aids -- it prevents the early-morning awakenings that plague many insomnia patients.

8-12 hours

Drug elimination phase begins but H1 receptor occupancy remains sufficient to support sleep. At the 3 mg dose, most individuals wake without significant residual sedation. At 6 mg, mild morning drowsiness is possible during the first few days of use but typically resolves.

1-2 weeks

Consistent nightly use establishes a reliable sleep pattern. Efficacy is maintained without tolerance development. No dose escalation needed, distinguishing doxepin from GABAergic sleep aids that often require increasing doses over time.

Side Effects & Safety

Common Side Effects

Morning drowsiness or grogginess (more common at the 6 mg dose; uncommon at 3 mg)
Dry mouth (mild at ultra-low doses, much less than at antidepressant doses)
Nausea
Upper respiratory tract infection (observed in clinical trials at rates similar to placebo)

Stop Signs - Discontinue if:

Signs of allergic reaction: rash, hives, swelling of the face, lips, or throat, difficulty breathing
Signs of serotonin syndrome: agitation, confusion, rapid heart rate, elevated body temperature, muscle rigidity
Severe or persistent morning drowsiness that impairs daily function
Irregular heartbeat, chest pain, or palpitations
Worsening depression or emergence of suicidal thoughts

Contraindications

Known hypersensitivity to doxepin or other dibenzoxepines
Concurrent use of MAOIs or use within 14 days of MAOI discontinuation
Untreated narrow-angle glaucoma
Severe urinary retention
Severe hepatic impairment (doxepin is extensively hepatically metabolized)

References

Efficacy and Safety of Doxepin 1 mg, 3 mg, and 6 mg in Adults with Primary Insomnia

Roth, T., Rogowski, R., Hull, S., et al.

Sleep (2007)

Randomized, double-blind, placebo-controlled trial demonstrating that doxepin at 1 mg, 3 mg, and 6 mg significantly improved sleep maintenance (wake after sleep onset) and total sleep time in adults with primary insomnia. The 3 mg and 6 mg doses showed the most robust improvements, with minimal next-day residual effects.
Low-Dose Doxepin for Insomnia: A Review of the Evidence

Krystal, A.D., Lankford, A., Durrence, H.H., et al.

Journal of Clinical Sleep Medicine (2011)

Comprehensive review of clinical evidence supporting ultra-low dose doxepin for insomnia. Confirmed that doxepin at 3-6 mg selectively targets H1 receptors without significant activity at muscarinic, adrenergic, or serotonergic receptors, resulting in effective sleep maintenance with a side effect profile comparable to placebo.
Doxepin 6 mg and Its Effect on Sleep in Elderly Patients with Primary Insomnia

Scharf, M., Rogowski, R., Hull, S., et al.

American Journal of Geriatric Psychiatry (2008)

Study in elderly patients (65+) with primary insomnia demonstrating that doxepin 1 mg and 3 mg significantly improved sleep maintenance. The low doses were well-tolerated in the elderly population with no significant next-day residual sedation, cognitive impairment, or falls risk, making it one of the safer insomnia treatments for older adults.
Long-Term Efficacy and Safety of Doxepin 3 mg and 6 mg in Elderly Subjects with Primary Insomnia

Krystal, A.D., Durrence, H.H., Scharf, M., et al.

Sleep (2010)

12-week study demonstrating sustained efficacy of ultra-low dose doxepin for insomnia in elderly subjects without evidence of tolerance, rebound insomnia, or withdrawal effects upon discontinuation. Confirmed the long-term safety and viability of doxepin as a non-habit-forming sleep maintenance aid.

Disclaimer

This information is for educational and research purposes only. Consult a healthcare professional before use.