What are the side effects of minoxidil?

Side Effects of Minoxidil

The most common side effects of topical minoxidil include scalp irritation, itching, and unwanted hair growth, while oral minoxidil can cause more serious cardiovascular effects including hypotension, reflex tachycardia, fluid retention, and potentially life-threatening circulatory shock. 1, 2

Topical Minoxidil Side Effects

Common Side Effects:

• Scalp reactions:
  • Itching and skin irritation of the treated area 1
  • Burning sensation, especially if the solution contacts the eyes 1
  • Contact dermatitis (both irritant and allergic types) 3

Less Common Side Effects:

• Unwanted hair growth:

  • Hypertrichosis (excessive hair growth), particularly on the face or other body parts 1
  • More common in women but generally reversible after discontinuation 1

• Hair-related effects:

  • Initial increased hair shedding due to synchronization of the hair cycle 3
  • Changes in hair color and/or texture 1

• Allergic reactions:

  • Some patients may develop allergic contact dermatitis to minoxidil itself 3
  • Reactions to propylene glycol (an inactive ingredient in some formulations) 3

Oral Minoxidil Side Effects

Oral minoxidil, primarily used for resistant hypertension, has more significant side effects:

Cardiovascular Effects:

• Hemodynamic effects:

  • Severe hypotension 2
  • Reflex tachycardia 4, 2
  • Potential to aggravate myocardial ischemia 4
  • Pericardial effusion (rare but serious) 4, 5
  • Circulatory shock (if ingested in large amounts) 2

• Fluid-related effects:

  • Significant sodium and water retention 4
  • Edema that may be debilitating 4
  • Acute pulmonary edema (in cases of overdose) 2

Other Significant Side Effects:

• Hypertrichosis (excessive hair growth) - nearly universal with oral use 5
• Left ventricular hypertrophy (with long-term use) 4
• Worsening of heart failure 2

Special Precautions

Contraindications:

• Women should not use the 5% topical solution (formulated for men) 1
• Not for use in children or babies 1
• Avoid use if:
  • Scalp is red, inflamed, infected, irritated, or painful 1
  • Hair loss pattern differs from androgenic alopecia 1
  • Hair loss is sudden or patchy 1
  • Patient has heart disease (consult doctor first) 1

Application Precautions:

• Apply only to the scalp, not other body parts 1
• Avoid contact with eyes 1
• Allow 4 hours before washing hair after application 1
• Allow sufficient drying time (2-4 hours) before bedtime 1
• Wash hands thoroughly after application 1

Management of Side Effects

• For scalp irritation: Discontinue use and consult a doctor if irritation persists 1
• For unwanted hair growth: Discontinue use; the effect is generally reversible 1
• For oral minoxidil cardiovascular effects:
  • Concomitant use of beta-blockers to control tachycardia 4, 5
  • Diuretics to manage fluid retention 4, 5
  • In cases of accidental ingestion or overdose, immediate medical attention is required with fluid resuscitation and vasopressor support 2

Efficacy Considerations

• Results with topical minoxidil may take 2-4 months to appear 1
• Hair regrowth stops when treatment is discontinued 1, 3
• Response varies between individuals 1
• For alopecia areata, higher concentrations (5% vs 1%) show better response rates 6

Minoxidil remains an effective treatment for hair loss and resistant hypertension when used appropriately, but the potential side effects require careful consideration and monitoring, particularly for the oral formulation.