Hexamethonium is a neuronal nAch (NN) receptor antagonist which acts in autonomic ganglia by binding mostly in or on the NN receptor, and not the acetylcholine binding site itself. It has no effect on the muscarinic acetylcholine receptors (mAChR) located on target organs of the parasympathetic nervous system, nor the nicotinic acetylcholine receptors at the neuromuscular junction (NM) that are responsible for skeletal muscle motor response.
It can act on receptors at pre-ganglionic sites in both the sympathetic and parasympathetic nervous system, which are both regulated (again, only pre-ganglionically) by nicotinic acetylcholine receptors. Postganglionic sympathetic systems are usually regulated by norepinephrine or adrenaline (adrenergic receptors), while parasympathetic systems are still acetylcholine based, but instead rely on muscarinic receptors (some post-ganglionic sympathetic neurons, such as those stimulating sweating, release acetylcholine).
The organ system and adverse effects of ganglion blockers are because both the parasympathetic and sympathetic stimuli are blocked at the preganglionic sites. Side effects include combined sympatholytic (e.g. orthostatic hypotension and sexual dysfunction) and parasympatholytic effects (e.g. constipation, urinary retention, glaucoma, blurry vision, decreased lacrymal secretion, dry mouth (xerostomia) effects. It was formerly used to treat disorders of the peripheral nervous system, such as chronic hypertension, which is innervated only by the sympathetic nervous system. The non-specificity of this treatment led to discontinuing its use 
The use of hexamethonium, an unapproved drug, in a normal volunteer during a medical study is believed to have caused her death.http://newsbreaks.infotoday.com/nbreader.asp?ArticleID=17534
Reference: Hardman et al., Goodman and Gilman's The Pharmacological Basis of Therapeutics, 10th edition, 2001, pp 210-211.