The so-called "magic pill" would be only effective when the magic was injected into a physical pill. Thylane had never told these nobles that she could actually induce her power into any object. The reason she chose pills was that it was easy for her to control her power, but it also made the nobles forget about the true nature of her ability.
In that party, Thylane had applied her ability to all the food and drinks. This was the only situation where the nobles would put their guard down.
It then appeared that people could also die of extreme pleasure as they died of pain. By the time the nobles realized what had happened, it was too late. They fell to the ground while holding their chests painfully as their bodies spasmed. Even those who did not overdose were also seriously impaired, their strength gone, with a mesmerized and dreamy look on their faces as though they were enjoying the most blissful moment in their life.