A recent unfortunate incident in the medical world leads to some interesting mathematics [1]. The incident centred around the half-life of a drug used in treating arthritic people; elderly patients having longer drug half-lives than young people, e.g. due to impaired liver or kidney function. Doses were being repeated before the half-life period of the patient, with a dangerous build-up of the drug in the system, leading to death in some cases. A mathematical model can be developed to describe the normal drug concentration variation with time, and the cumulative effect of repeated doses.