The Unstable Medium

According to the artisans, trace amounts of Crimson Marrow are not enough to induce hallucinations in adults, so they cut it into extremely thin flakes to use as a medium for powering Legacies. By the artisans' estimates, a piece of Crimson Marrow the size of a fingernail is enough to keep a large-scale Bapharian Legacy like the "Orb Synthesizer" running for about a year.
Recently, however, this delicate balance has been disrupted, and the previously stable marrow flakes have begun to exhibit hallucinogenic side effects.
Coincidentally, a similar situation arose on the alchemists' side: hallucinogenic effects actually began to manifest in sedatives they'd synthesized using their normal methods.
Putting that together with the Creed's meaningful reminder that "that stuff has been changing lately," perhaps the answer is already blatantly obvious.
What is changing may not be our usage of it, but the substance itself.