Dowdell, Thomas, Suresh Govindaraj, and Prem Jain. "The Tylenol Incident, Ensuing Regulation, and Stock Prices." Journal of Financial and Quantitative Analysis, June 1992.

This event study reviews daily stock returns for Johnson & Johnson and 28 other healthcare firms for 28 days (2 prior to the Tylenol incident, 25 after). During the first nine days, only Johnson & Johnson had abnormal returns (-29%, t=-3.5). In the following 19 days, regulations were imposed. Other drug stocks were then affected (-12%, t=-4.0).