Tricyclics for insomnia

Low doses (sub-therapeutic for depression) of sedating tricyclics, particularly amitriptyline, have been used for decades to treat insomnia

• particularly common practice in primary care in the UK, where amitriptyline 10 or 25 mg is also used for long periods in many patients with chronic illness, particularly those with pain syndromes
  
  
• at 10 or 25mg dose, amitriptyline is probably acting mostly as a histamine H1 receptor antagonist although a degree of 5-HT2 and cholinergic muscarinic antagonism may
  also contribute
  
  
• no controlled studies of hypnotic efficacy of low-dose amitriptyline in insomnia, and tricyclics are more likely to be lethal than licensed hypnotics in overdose
  
  
• controlled trials demonstrate an effect of doxepin in insomnia at sub-antidepressant dose (25 mg) for four weeks, with rebound insomnia

A review stated (2):

• "..limited data analysis with two medications at particular doses (most studies included extremely low doxepin), we assert that tricyclic antidepressants (TCA)s can be an effective pharmacological treatment for insomnia. TCAs were found to improve sleep outcome measures, with the notable exception of an 82% increase in somnolence. Overall TCAs have very problematic and dangerous side effects, while TCAs were not found to increase the dropout rate compared with the placebo.."

Reference:

• Wilson S et al. British Association for Psychopharmacology consensus statement on evidence-based treatment of insomnia, parasomnias and circadian rhythm disorders: An update. J Psychopharmacol. 2019 Aug;33(8):923-947
• Liu Y et al. reatment of insomnia with tricyclic antidepressants: a meta-analysis of polysomnographic randomized controlled trials.Sleep Med. 2017 Jun;34:126-133