Involuntary movements (of the mouth, face, and limbs), nightmares, low blood pressure when a person stands up (orthostatic hypotension), constipation, nausea, drowsiness, confusion, hallucinations, paranoia, palpitations, and flushing

Dopamine agonists

Severe nausea, vomiting, and lumps (nodules) under the skin at the injection site

Drowsiness, nausea, light-headedness (due to orthostatic hypotension), confusion, obsessive-compulsive behavior, new or increased urges (such as gambling), and hallucinations

When these medications are suddenly stopped, neuroleptic malignant syndrome

dopamine

Drowsiness, nausea, light-headedness (due to orthostatic hypotension), confusion, obsessive-compulsive behavior, new or increased urges (such as gambling), hallucinations, weight gain (possibly due to fluid retention), and sometimes skin irritation where the patch is applied

MAO-B inhibitors

Nausea, insomnia, drowsiness, and swelling due to fluid accumulation (edema)

COMT inhibitors

Diarrhea, back pain, and orange urine

Anticholinergic medications*

Drowsiness, confusion, dry mouth, blurred vision, dizziness, constipation, difficulty urinating, loss of bladder control, and impaired regulation of body temperature

Anticholinergic medications may be given alone in the early stages to young people whose most troublesome symptom is tremor. These medications can reduce tremor but do not affect slow movements or relieve muscle stiffness.

Doctors try to avoid using these medications in older adults because the side effects are particularly troublesome for older adults.

Antiviral medication

Nausea, dizziness, insomnia, anxiety, confusion, edema, difficulty urinating, worsening of glaucoma, and mottled discoloration of the skin due to dilated blood vessels (livedo reticularis)

Amantadinelevodopa.