The pill in question is called a lozenge, which is a very non-descriptive name. It's almost a synonym to "candy".
Lozenge is focus drug, and, as you can guess, it improves your ability to focus.
Lozenges is inserted orally and the user must suck on it for its
effect to persist. One pill only lasts a few minutes.
The user is granted greater awareness, making it possible to better
watch even small change in expression. For this reason, Martian naval
intelligence uses this drug during interrogation.
The usage of Lozenge is easy to spot, as the pupils of the person
using it contract to tiny point.
Information found in the Novel Leviathan Wakes, in Chapter 11.