Why does high blood pressure medicine tell you to stay out of the sun? What harm can it do?

Certain antihypertensives cause a sensitivity to ultraviolet rays. You will sunburn easier, and in extfreme cases, develop other, related skin conditions.

Applying a sunblock lotion is often sufficient protection.

Please note that this side effect does not affect all patients.

This is from Methyclorothiazide
ADVERSE REACTIONS SIGNIFICANT
1% to 10%:
Cardiovascular: Orthostatic hypotension
Dermatologic: Photosensitivity
Endocrine & metabolic: Hypokalemia
Gastrointestinal: Anorexia, epigastric distress

<1% (Limited to important or life-threatening): Agranulocytosis, aplastic anemia, cutaneous vasculitis, erythema multiforme, hemolytic anemia, hepatic function impairment, hypercalcemia, leukopenia, necrotizing angiitis, pancreatitis, respiratory distress, Stevens-Johnson syndrome, thrombocytopenia, vasculitis

CONTRAINDICATIONS 鈥?Hypersensitivity to methyclothiazide or any component, thiazides, or sulfonamide-derived drugs; anuria; renal decompensation

WARNINGS / PRECAUTIONS
Concerns related to adverse effects:

Electrolyte disturbances: Hypokalemia, hypochloremic alkalosis, and hyponatremia can occur.
Photosensitivity: Photosensitization may occur.
Sulfa allergy: Chemical similarities are present among sulfonamides, sulfonylureas, carbonic anhydrase inhibitors, thiazides, and loop diuretics (except ethacrynic acid). Use in patients with thiazide or sulfonamide allergy is specifically contraindicated in product labeling, however, a risk of cross-reaction exists in patients with allergy to any of these compounds; avoid use when previous reaction has been severe. Discontinue if signs of hypersensitivity are noted.

Ask your pharmacist it depends which high blood pressure medication you are taking, some have different side effect, some sz that you can not eat grapefruit and some you can not drink milk. you even can look it up in the internet.

Google Skin Atrophy, the blood vessels near the surface of the skin can become dilated, and along with the sun, this can cause all kinds of problems like Rosacea and who knows what else.

It contributes to skin cancer - even worse than just the sun alone.

Getting too hot messes with your blood pressure & can make you pass out.