A pill was a method to administer medicine.
By the time of the presidency of the Fourth Doctor, the Time Lords had long lost the habit of feeding with raw or complex food, using freeze-dried pills instead. (TV: The Invasion of Time)
The personal destructor was composed of modulated black star matter within a tasteless pill. When swallowed, the pill would attach itself to the host's digestive tract, eventually activating when sufficiently stressed. It would then explode with the force of thousands of scatter bombs. (AUDIO: Bang-Bang-a-Boom!)
Adipose pills were used by Adipose Industries for the propagation of the Adipose species. (TV: Partners in Crime)
Retcon pills were used by Torchwood Three to erase the memories of people that had witnessed alien activities. (TV: They Keep Killing Suzie, Something Borrowed)