What are the most dangerous drug-drug interactions to know?

The most dangerous drug interactions include warfarin with NSAIDs causing severe bleeding, MAOIs with SSRIs causing serotonin syndrome, opioids with benzodiazepines causing fatal respiratory depression, methotrexate with NSAIDs causing methotrexate toxicity, potassium-sparing diuretics with ACE inhibitors causing hyperkalemia, and digoxin with amiodarone causing digoxin toxicity. Fluoroquinolones with corticosteroids increase tendon rupture risk. Statins with certain macrolides and antifungals increase rhabdomyolysis risk.