Contraindications — 30 Common Drugs

A contraindication means the expected harm generally outweighs benefit in that setting; a precaution means the drug may still be used after risk mitigation. Always distinguish the two.

• Metformin: avoid in severe renal failure (eGFR <30 mL/min/1.73 m²) and temporarily with acute hypoxia/shock or severe illness that increases lactic-acidosis risk.
• ACEI/ARB: avoid in pregnancy; do not use in bilateral renal-artery stenosis with haemodynamically significant disease; stop/review for severe hyperkalaemia or major creatinine rise.
• Spironolactone: avoid with significant hyperkalaemia and use very cautiously in advanced renal impairment.
• Beta-blocker: severe bradycardia, high-grade AV block without pacing and cardiogenic shock are key contraindications; asthma is drug/selectivity/context dependent rather than a blanket rule.
• Verapamil/diltiazem: avoid in HFrEF and significant bradycardia/AV block; combining with beta-blockade can precipitate profound bradycardia.
• Nitrates: avoid with recent PDE5 inhibitor use and in marked hypotension; use caution in preload-dependent states.
• NSAIDs: avoid or minimise in active GI bleeding, severe renal dysfunction, decompensated HF and certain high-risk cardiovascular settings.
• Statins: contraindicated in pregnancy; active severe liver injury requires reassessment, while stable chronic liver disease is not automatically a contraindication.
• Methotrexate: pregnancy, significant marrow suppression and severe hepatic/renal dysfunction are major red flags; dosing errors can be fatal.
• SGLT2 inhibitor: hold during major acute illness, prolonged fasting or surgery because of euglycaemic DKA risk; not a treatment for type 1 diabetes in routine practice.
• Combined estrogen contraceptive: avoid in important thrombotic-risk states, migraine with aura, and certain smokers/vascular-risk profiles.
• Tetracyclines: generally avoid during pregnancy and in young children when safer alternatives exist; indication-specific exceptions require specialist judgement.

Check indication, dose, organ function, pregnancy status, ECG/electrolytes where relevant, and whether the risk is class-wide or agent-specific.