Age * Senile<unk>  (a reduction in the size of a person's pupil in old age) Diseases * Horner's syndrome * Hemorrhage into pons (intracranial hemorrhage) * Hereditary disorders * Cluster Headaches with ptosis * Iridocyclitis * Fatal familial insomnia * Aphakia Drugs * Opioids such as fentanyl, morphine, heroin and methadone (the notable exception being pethidine) * Products containing nicotine such as cigarettes, chewing tobacco or gum. * Imidazolines such as clonidine, naphazoline, oxymetazoline and tetrahydrozoline * Antipsychotics, including risperidone, haloperidol, chlorpromazine, olanzapine, quetiapine * Cholinergic agents such as acetylcholine * Acetylcholinesterase inhibitors * Serotonin antagonists, such as Ondansetron (an anti-emetic) known by its brand name Zofran * Some cancer chemotherapy drugs, including camptothecin derivatives * Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA) * Some MAO Inhibitors. * Pilocarpine eye drops and all other parasympathomimetics * In some rare cases, when exposed to mustard gas * Organophosphates
Miosis
Sniffing 
Dryness 
Picardy sweat
Morphea
Drooling
Orgasm
Myalgia