Not sure why this book has been knocking around in my memory for a few weeks. I read it ~25 years ago, the details are very sketchy. The setting is Earth, sometime in the future. The world is faced with severe overpopulation, but there's a plan to reduce the population. Everyone will take a pill, and some portion of the pills are poison. The poison pills are randomly distributed, so you don't know if you were going to die or not. Then I really don't know what happened! Does this ring a bell to anyone?