Platelets, also called thrombocytes (thromb- + -cyte, blood clot cell), are a component of blood whose function (along with the coagulation factors) is to stop bleeding by clumping and clotting blood vessel injuries.
Milk of the poppy is essentially the Westeros version of morphine. Maesters make it from crushed poppy flowers, and morphine and other opiate-based drugs are made from poppy plants. Indeed, the books' descriptions strongly suggest that the poppy is intended to be the real-world opium poppy (Papaver somniferum).
Trivia. 1  It's theorized before Poppy became queen of the trolls, her mother was also queen, but she probably sacrificed herself for her daughter and subjects. 2  Considering that she was a toddler when the trolls escaped from Bergen town, Poppy is in her early twenties by the events of the film.