What are the potential side effects of Minoxidil (minoxidil) in patients with androgenetic alopecia, especially those with a history of cardiovascular disease?

Minoxidil Side Effects

The most common side effects of minoxidil are hypertrichosis (unwanted body/facial hair growth), scalp irritation, and cardiovascular symptoms including tachycardia and hypotension, with topical formulations being significantly safer than oral formulations, especially in patients with cardiovascular disease. 1, 2

Topical Minoxidil Side Effects

Local/Dermatologic Effects

• Scalp irritation, itching, and redness are the most common adverse effects of topical minoxidil, occurring primarily due to the alcohol and propylene glycol vehicle rather than minoxidil itself 1, 3, 4
• Allergic and irritant contact dermatitis can develop, with 41% of patients using alcohol-based formulations reporting adverse events compared to only 9% with cetosomal (alcohol-free) formulations 3
• Temporary increased hair shedding may occur during the first 2 weeks of treatment as old hairs are replaced by new growth—this is expected and indicates the medication is working 1

Systemic Effects from Topical Use

• Unwanted facial and body hair growth (hypertrichosis) can occur if the medication spreads beyond the scalp, though this is rare and reversible with discontinuation 1, 4
• To minimize hypertrichosis risk: limit application only to the scalp, wash hands immediately after application, and allow 2-4 hours drying time before bed 1
• Cardiovascular symptoms (chest pain, rapid heartbeat, faintness, dizziness) are rare with topical use but require immediate discontinuation and medical evaluation 1

Oral Minoxidil Side Effects

Common Dose-Dependent Effects (Type A)

• Hypertrichosis occurs in the majority of patients on oral minoxidil, with women significantly more prone than men 2, 5
• Cardiovascular symptoms including tachycardia (3.5% at high doses), hypotension, and edema are dose-dependent 2, 5
• Fluid retention and weight gain can occur, as demonstrated in a case report where a patient gained weight and developed edema that resolved 2 weeks after discontinuation 6
• Facial flushing and breathlessness may develop 6

Serious Idiosyncratic Effects (Type B)

• Pericardial effusion is a rare but serious idiosyncratic reaction that can occur unpredictably 7, 2
• The American College of Cardiology explicitly recommends avoiding oral minoxidil in patients with existing cardiovascular conditions 7
• Myocardial infarction has been reported in 1 of 14 documented overdose cases 6

Dose-Related Considerations

• Low-dose oral minoxidil (≤5 mg/day) has better tolerability than higher doses 2
• At doses >5 mg/day, 24.6% of patients experienced adverse effects, with 17.5% developing hypertrichosis and 3.5% experiencing tachycardia 5
• Women require lower starting doses (0.5-1 mg/day) due to significantly higher incidence of adverse effects compared to men (1-5 mg/day starting dose) 7, 2

Overdose and Emergency Situations

Acute Toxicity Profile

• Minoxidil overdose causes hypotension and/or tachycardia in all reported cases, occurring within 6 hours of ingesting 100-3000 mg 6
• Systemic symptoms have occurred after ingestion of topical formulations (10 of 14 cases), tablet ingestion (3 of 14 cases), and excessive topical application to scalp (1 of 14 cases) 6
• Standard fluid therapy is ineffective for minoxidil-induced hypotension—peripherally acting alpha-adrenergic agonists (phenylephrine, midodrine, norepinephrine) are preferred over dopamine and epinephrine 6

Cardiovascular Disease Considerations

Pre-Treatment Screening

• All patients must be screened for cardiovascular disease before initiating oral minoxidil 7
• No cardiovascular screening is required before starting topical minoxidil 7

Monitoring Requirements for Oral Minoxidil

• Monitor orthostatic vital signs, edema, heart rate and rhythm, and cardiovascular symptoms at each visit 7
• Patients with pre-existing cardiovascular conditions should avoid oral minoxidil entirely due to rare but serious adverse effects including pericardial effusion 7

Important Safety Warnings

Contraindications

• Women should not use 5% topical minoxidil as it works no better than 2% formulation and may cause facial hair growth 1
• Minoxidil is contraindicated during pregnancy and breastfeeding as it may be harmful 1
• Do not use in children under 18 years of age 1
• Avoid application to inflamed, infected, irritated, or painful scalp 1

Critical Safety Points

• Minoxidil is flammable—keep away from fire or flame 1
• Avoid eye contact; if accidental contact occurs, rinse with large amounts of cool tap water 1
• Sudden cessation of oral minoxidil can cause severe rebound hypertension (though this applies to high-dose antihypertensive use, not low-dose hair loss treatment) 8
• Discontinue immediately if chest pain, rapid heartbeat, faintness, dizziness, sudden unexplained weight gain, or swelling of hands/feet occurs 1