We know who took the elixir: Robert, Sophia, Victor, Rufus.
Robert took it while he was asleep (even before) When he woke up he was evil (I know it was because of Caroline's negative influence) but he still took a massive dose of the potion for years.
Sophia has taken the essence for years, almost a century, as much as Robert had taken it. She looks like she has lost control as if she has been possessed. Robert has been asleep for years, so this transformation never completely happened.
Victor does not seem to have taken it in excessive doses, it is clear that knowing that he could not replicate it, he used what was available to him with measure, a small dose every now and then. If you notice it is the one most controlled by elixir drinkers.
Rufus is the same age as Victor, but he looks much younger. it is certain that he started taking the elixir around the same time as Victor, in much larger doses. For years he held control, he was the Osirian he had protection in himself, but when the next Osirian was born (aka Eddie) Rufus slowly started to lose control and reason. I bet he betrayed society at that time.
I know that among the drinkers are the members of society, namely Mr Sweet and Mrs Andrews, but if they took it in smaller quantities anyway, Victor had to share what little he had.
