Dry mouth in the context of Polypharmacy

Multiple system atrophy (MSA) is a rare neurodegenerative disorder characterized by tremors, slow movement, muscle rigidity, postural instability (collectively known as parkinsonism), autonomic dysfunction and ataxia. This is caused by progressive degeneration of neurons in several parts of the brain including the basal ganglia, inferior olivary nucleus, and cerebellum. MSA was first described in 1960 by Milton Shy and Glen Drager and was then known as Shy–Drager syndrome.

Many people affected by MSA experience dysfunction of the autonomic nervous system, which commonly manifests as orthostatic hypotension, impotence, loss of sweating, dry mouth and urinary retention and incontinence. Palsy of the vocal cords is an important and sometimes initial clinical manifestation of the disorder.

Pseudoephedrine, sold under the brand name Sudafed among others, is a sympathomimetic medication which is used as a decongestant to treat nasal congestion. It has also been used off-label for certain other indications, like treatment of low blood pressure. At higher doses, it may produce various additional effects including stimulant, appetite suppressant, and performance-enhancing effects. In relation to this, non-medical use of pseudoephedrine has been encountered. The medication is taken by mouth.

Side effects of pseudoephedrine include insomnia, elevated heart rate, increased blood pressure, restlessness, dizziness, anxiety, and dry mouth, among others. Rarely, pseudoephedrine has been associated with serious cardiovascular complications like heart attack and hemorrhagic stroke. Some people may be more sensitive to its cardiovascular effects. Pseudoephedrine acts as a norepinephrine releasing agent, thereby indirectly activating adrenergic receptors. As such, it is an indirectly acting sympathomimetic. Pseudoephedrine significantly crosses into the brain, but has some peripheral selectivity due to its hydrophilicity. Chemically, pseudoephedrine is a substituted amphetamine and is closely related to ephedrine, phenylpropanolamine, and amphetamine. It is the (1S,2S)-enantiomer of β-hydroxy-N-methylamphetamine.

Benzodiazepine withdrawal syndrome (BZD withdrawal) is the cluster of signs and symptoms that may emerge when a person who has been taking benzodiazepines as prescribed develops a physical dependence on them and then reduces the dose or stops taking them without a safe taper schedule.

Typically, benzodiazepine withdrawal is characterized by sleep disturbance, irritability, increased tension and anxiety, depression, panic attacks, hand tremor, shaking, sweating, difficulty with concentration, confusion and cognitive difficulty, memory problems, dry mouth, nausea and vomiting, diarrhea, loss of appetite and weight loss, burning sensations and pain in the upper spine, palpitations, headache, nightmares, tinnitus, muscular pain and stiffness, and a host of perceptual changes. More serious symptoms may also occur such as depersonalization, restless legs syndrome, seizures, and suicidal ideation.

Bupropion, formerly called amfebutamone, and sold under the brand name Wellbutrin among others, is an atypical antidepressant that is indicated in the treatment of major depressive disorder and seasonal affective disorder and to support smoking cessation. A norepinephrine–dopamine reuptake inhibitor (NDRI), it is also popular as an add-on medication in the cases of "incomplete response" to the first-line selective serotonin reuptake inhibitor (SSRI) antidepressant. Bupropion has several features that distinguish it from other antidepressants: It does not usually cause sexual dysfunction, it is not associated with weight gain and sleepiness, and it is more effective than SSRIs at improving symptoms of hypersomnia and fatigue. Bupropion, particularly the immediate-release formulation, carries a higher risk of seizure than many other antidepressants; hence, caution is recommended in patients with a history of seizure disorder. The medication is taken by mouth.

Common adverse effects of bupropion with the greatest difference from placebo are dry mouth, nausea, constipation, insomnia, anxiety, tremor, and excessive sweating. Raised blood pressure is notable. Rare but serious side effects include seizures, liver toxicity, psychosis, and risk of overdose. Bupropion use during pregnancy may be associated with increased likelihood of congenital heart defects.

Ketanserin, sold under the brand name Sufrexal, is an antihypertensive agent which is used to treat arterial hypertension and vasospastic disorders. It is also used in scientific research as an antiserotonergic agent in the study of the serotonin system; specifically, the 5-HT₂ receptor family. The drug is taken by mouth.

Side effects of ketanserin include dizziness, tiredness, edema, dry mouth, weight gain, and QT interval prolongation. Ketanserin acts as a selective antagonist of the serotonin 5-HT_2A, α₁-adrenergic, and histamine H₁ receptors. It also shows lower affinity for various other targets.