Hypo- and hypersalivation induced by psychoactive drugs - Incidence, mechanisms and therapeutic implications

Psychoactive drugs can have profound effects On salivation: apart from affe cting the amount of saliva secreted (i.e. causing either hypo- or hypersali vation), they may also modify the composition of the saliva, Hyposalivation leads to the subjective experience of 'dry mouth' (xerostomia) which, in a ddition to causing subjective discomfort. may be associated with dental car ies and oral infections. On the other hand. hypersalivation leads to 'drool ing' (sialorrhoea), which can hr a source of social embarrassment and can b e associated with Parotitis, choking and even aspiration pneumonia. Both xe rostomia and sialorrhoea can impair patient compliance. Antidepressants [tr icyclic antidepressants. noradrenaline (norepinephrine) reuptake inhibitors ]. lithium, antipsychotics of the phenothiazine class and alpha(2)-adrenoce ptor agonists (e.p. clonidine and lofexidine) are commonly associated with hyposalivation and xerostomia, whereas both classical and novel antipsychot ics can cause sialorrhoea. However, only clozapine-induced sialorrhoea, occ urring in about 30% of patients treated uith the drug, is of any major clin ical significance. The salivary glands receive a dual sympathetic (noradrenergic) and parasymp athetic (cholinergic) innervation, and psychoactive drugs may affect either the gland cells themselves or their neural control. The effects of psychoa ctive drugs on the autonomic control of salivation is mediated via their mu ltiple actions at neuroreceptors and synaptic mechanisms. Blockade of musca rinic cholinoceptors and alpha(1)-adrenoceptors. inhibition of noradrenalin e uptake and stimulation of alpha(2)-adrenoceptors may lead to hyposalivati on. whereas stimulation of muscarinic cholinoceptors and dopamine D-2 recep tors, blockade of alpha(2)-adrenoceptors and depletion of noradrenaline fro m central stores may result in hypersalivation. It is important that the clinician is familiar with the effect of each clas s of drug on salivation. so that he/she can mitigate these by the judicious choice of drug and dosage schedule. and. if necessary. by providing sympto matic treatment for these distressing, and occasionally dangerous, adverse effects.