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

Psychoactive drugs can have profound effects On salivation: apart from affecting the amount of saliva secreted (i.e. causing either hypo- or hypersalivation), they may also modify the composition of the saliva, Hyposalivation leads to the subjective experience of 'dry mouth' (xerostomia) which, in addition to causing subjective discomfort. may be associated with dental caries and oral infections. On the other hand. hypersalivation leads to 'drooling' (sialorrhoea), which can hr a source of social embarrassment and can be associated with Parotitis, choking and even aspiration pneumonia. Both xerostomia and sialorrhoea can impair patient compliance. Antidepressants [tricyclic antidepressants. noradrenaline (norepinephrine) reuptake inhibitors]. lithium, antipsychotics of the phenothiazine class and alpha(2)-adrenoceptor agonists (e.p. clonidine and lofexidine) are commonly associated with hyposalivation and xerostomia, whereas both classical and novel antipsychotics can cause sialorrhoea. However, only clozapine-induced sialorrhoea, occurring in about 30% of patients treated uith the drug, is of any major clinical significance. The salivary glands receive a dual sympathetic (noradrenergic) and parasympathetic (cholinergic) innervation, and psychoactive drugs may affect either the gland cells themselves or their neural control. The effects of psychoactive drugs on the autonomic control of salivation is mediated via their multiple actions at neuroreceptors and synaptic mechanisms. Blockade of muscarinic cholinoceptors and alpha(1)-adrenoceptors. inhibition of noradrenaline uptake and stimulation of alpha(2)-adrenoceptors may lead to hyposalivation. whereas stimulation of muscarinic cholinoceptors and dopamine D-2 receptors, blockade of alpha(2)-adrenoceptors and depletion of noradrenaline from central stores may result in hypersalivation. It is important that the clinician is familiar with the effect of each class 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 symptomatic treatment for these distressing, and occasionally dangerous, adverse effects.