It is the histaminiergic (H1), muscarinic acetylcholinergic (M1), and alpha adrenergic (α1) blockade that is responsible for the side-effects of TCAs. These include somnolence and lethargy, anticholinergic side-effects, and hypotension. Due to the narrow gap between their ability to block the biogenic amine uptake pumps versus the inhibition of fast sodium channels, even a modest overdose of one of the TCAs could be lethal. TCAs were, for 25 years, the leading cause of death from overdoses in many countries. Patients being treated with antidepressants are prone to attempt suicide and one method they use is to take an overdose of their medications.