Doxepin
Also known as: Silenor, Sinequan
Tricyclic Antihistamine | Ultra-Low Dose Sleep Aid
Overview
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.
Key benefits
- FDA-approved specifically for sleep maintenance insomnia at ultra-low doses (3-6 mg as Silenor)
- Highly selective H1 antihistamine at low doses, avoiding the side effects of traditional tricyclic antidepressants
- Non-habit-forming with no dependence, tolerance, or abuse potential
- No rebound insomnia upon discontinuation, unlike benzodiazepines and Z-drugs
- Particularly effective for maintaining sleep in the latter half of the night, when many other sleep aids have worn off
- Extremely well-tolerated side effect profile at ultra-low doses
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.
Molecular data
- Type
- Tricyclic dibenzoxepin derivative (C19H21NO)
- Half-life
- ~15 hours
Indications
What the research community uses this compound for, with self-reported effectiveness.
FDA-Approved
Off-Label
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Delivery method
| Protocol | Dose | Frequency | Duration |
|---|---|---|---|
| — | 3 mg | Once at bedtime | — |
| — | 6 mg | Once at bedtime | — |
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
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)
Rare side effects
- Allergic reactions including skin rash or urticaria
- Serotonin syndrome (primarily a concern at antidepressant doses or when combined with serotonergic drugs)
- Cardiac arrhythmias or QT prolongation (a concern at antidepressant doses; negligible at ultra-low doses)
- Worsening of narrow-angle glaucoma (anticholinergic effect, primarily at higher doses)
- Urinary retention (anticholinergic effect, primarily at higher doses)
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)
Monitoring
- Daytime alertness: assess for residual next-morning drowsiness, particularly during the first week and at the 6 mg dose
- Mental status: monitor for worsening depression or suicidal ideation (standard TCA warning, though less clinically relevant at ultra-low doses)
- Hepatic function: periodic monitoring if used long-term in patients with hepatic impairment
- Drug interactions: review medication list for CYP2D6 inhibitors that may increase doxepin levels
References
Primary literature and clinical-trial data informing this entry.