Darvocet became a subject of serious safety concerns. Clinical studies revealed that propoxyphene could cause dangerous changes in heart rhythm, even when taken at recommended doses. These cardiac risks increased the likelihood of severe complications, including potentially fatal arrhythmias. Additionally, like other opioid medications, Darvocet carried risks of dependence, overdose, and adverse side effects such as dizziness, drowsiness, nausea, and constipation.