Aspirated pills containing active drug ingredients (alcali (PMID 26878260), drugs or metals (e.g. iron) may cause severe airway injury known as the 'Pill Aspiration Syndrome'. Release of iron sulfate or other drugs from aspirated tablets can cause caustic airway or esophageal injury. On histopathology, the iron can be evidenced using special stains. Alendronate, sucralfate and metformine may cause similar problems. Reviews and causative drug pills at PMID 23918109 & 25560862