The medkit is marked with the words "NPR-21p antiradiation kit (test model)". The directions contain a huge list of rather unpleasant side-effects.
― In-game description
The NPR-21p special medkit is a mission item in S.T.A.L.K.E.R.: Clear Sky.
Description[]
Visually identical to the army medkit, this unique test model is seemingly able to cure heavy wounds, but has a large amount of side effects, due to its test nature. This medkit must be obtained as part of the Deliver a special medkit side mission. The Loner who provides this mission states that it is the only medkit which would be able to heal a friend of his that was wounded by anomalies. The medkit is guarded by the army in the Military checkpoint in the Cordon, making it quite difficult to obtain.
This medkit, much like other quest items, isn't usable by the player.
