Blood thinners + NSAIDs
Warfarin or aspirin combined with ibuprofen or naproxen increases bleeding risk. Use paracetamol for pain unless your doctor approves otherwise.
Antibiotics + oral contraceptives
Some antibiotics (rifampin) reduce birth control effectiveness. Use a backup method during and for 7 days after treatment.
Grapefruit juice
Inhibits the enzyme that breaks down many drugs (statins, blood pressure meds, some immunosuppressants), causing dangerously high blood levels.
Herbal supplements
St. John's Wort affects antidepressants and birth control; ginkgo and garlic increase bleeding risk; always tell your doctor what supplements you take.
Safe practices
Use one pharmacy so all your prescriptions are checked together, keep an up-to-date medication list, and read labels carefully before taking anything new.