Persona suppressors were used by Strega as well as by Shinjiro Aragaki. Stopping the use of the drug could result in a Persona User's Persona killing them. The reason for this is that the members of Strega awakened their Personas through unnatural means. According to an answer to a fan question sent to the Persona Stalker Club, they can also cause the body to become unable to regulate body temperature, hence why Shinjiro is always wearing a coat and hat.