Cultural Question

I have become so so so hooked on this series to the point that I have watched it in two different translations in one week! However, I am wondering about one thing. In both translations the bottle that Jiang Xiaoshuai purchases is just translated as "essence" and I was wondering if anyone could tell me what it actually is. Based on the context and effect I had assume it was something similar to poppers but I'd love to know for sure.