TABLE 1.

Characteristics of Medications Tried for OH

Medication	Mechanism of Action	Dose Range	Contraindications	Side Effects
Atomoxetine	A selective norepinephrine reuptake inhibitor, increasing norepinephrine available in the synapse	18 mg used in trials (OD) Not licensed for OH in United Kingdom	Phaeochromocytoma; severe cardiovascular disease; and severe cerebrovascular disease	Anxiety: appetite decreased; asthenia; chills (in adults); constipation; depression; dizziness; drowsiness; gastrointestinal discomfort; headaches; hyperhidrosis; menstrual cycle irregularities; altered mood); nausea); prostatitis; sexual dysfunction; thirst; vomiting; and weight loss
Caffeine	Wide ranging and poorly understood mechanism—thought to stimulate catecholamine release causing vasoconstriction (when used irregularly)	100 mg used (OD)	No absolute CI, caution advised with history of severe anxiety; cardiovascular disease or symptomatic arrhythmias; peptic ulcer disease or gastroesophageal reflux disease	Restlessness and shakiness, insomnia, headaches, dizziness, tachycardia, dehydration, and anxiety
Droxidopa (L-DOPS)	A norepinephrine precursor, which is metabolised in the brain, allowing the norepinephrine to act on α-adrenergic receptors causing vasoconstriction and on beta-adrenergic receptors to stimulate heart contraction and dilate arteries	100–600 mg (TDS) Not available in United Kingdom	Neuroleptic malignant syndrome, supine hypertension, coronary artery disease, arrhythmia, chronic heart failure	Nausea, headache, increased blood pressure, hallucination, and anorexia
Ergometrine	An ergot alkaloid, which causes arterial vasoconstriction by stimulation of α-adrenergic and serotonin receptors as well as inhibiting the release of endothelial-derived relaxation factor	1 mg used in trials (OD) Licensed for 250–500 μg in postpartum haemorrhage	Eclampsia; first stage of labor; induction of labor; s stage of labor; sepsis; severe cardiac disease; severe hypertension; vascular disease	Abdominal pain; arrhythmias; chest pain; coronary vasospasm; dizziness; dyspnoea; headache; hypertension; myocardial infarction; nausea; palpitations; pulmonary edema; rash; tinnitus; vasoconstriction; and vomiting
Midodrine	A prodrug that is converted into desglymidodrine, which works on α1-adrenergic receptors to increase vascular tone	2.5–10 mg TDS	Aortic aneurysm; blood vessel spasm; bradycardia; cardiac conduction disturbances; cerebrovascular occlusion; congestive heart failure; hypertension; hyperthyroidism; myocardial infarction; narrow-angle glaucoma; proliferative diabetic retinopathy; serious prostate disorder; urinary retention	Chills; flushing; gastrointestinal discomfort; headache; nausea; paraesthesia; piloerection; scalp pruritus; supine hypertension (dose-dependent); and urinary disorders
Pyridostigmine	An anticholinesterase that reduces the breakdown of acetylcholine in the synaptic cleft	60 mg used in trials (30 mg BD/60 mg OD) 30–120 mg licensed for multiple sclerosis	Intestinal obstruction; urinary obstruction	Abdominal cramps; diarrhoea; excessive tearing; hypersalivation; nausea; and vomiting
Yohimbine	Presynaptic α2-adrenergic receptor antagonist, which may lead to increased norepinephrine release	2–5.4 mg (TDS) used in clinical trials	Pregnancy, hypersensitivity, children, and panic disorder	Anxiety; irritability; headache; sweating; nausea; tachycardia; priapism; worsening of panic attacks; vomiting; dizziness; nervousness; restlessness; reduced urination; hypertension; tremors; and skin flushing