I'm not usually interested in the chemical ways that the fighting experience can be enhanced or improved upon, but I found this 2016 study that Tylenol dampens one's empathy towards the pain of others provocative. It was not only the physical pain of others, but also their social pain. "From painkiller to empathy killer: acetaminophen (paracetamol) reduces empathy for pain" (2016). The effect was not pronounced, this interview on the subject suggests maybe a 10% reduction: "Researchers Examine Why Tylenol Affects Empathy" (2016) (the study seems to indicate something along the lines of 5-8% maybe), but it does present a really interesting side-effect for a very common over the counter drug.
I can't imagine that experienced fighters would benefit much from this as overcoming the psychological impact of the potential pain of others is a large part of developing as a fighter, but it does make some sense that 2 Tylenol might be worth taking if you are having a first fight, or even a fight in the first 10. Maybe that 10% difference in empathy threshold could mean something to you. (Note: even though it is an over the counter drug Tylenol in larger doses can wreck your liver and even be life threatening. This is not something you want to pound.) The idea might be to dull your own pain, a bit, and your sensitivity to the pain of others.
It's super interesting that some of the theorizing about why a drug might reduce both involves the way that pain is modeled, that there is some sense in which the mechanism by which we feel our own pain is also involved in our feeling for, virtually experiencing, the pain of others.
While people who are drawn to fighting often imagine that there shouldn't be an issue here, there really can be lots of difficulty in not only hurting others, but also the humiliation given to them by making them look bad, or giving a loss. Sure, lots of fighters can take on hyper-aggressive persona which act like they don't care, but underappreciated is that many people who are drawn to fighting are quite sensitive, and many are wounded themselves. The ability to negotiate the domination of others, the hurting of others, can involve a great deal of personal development. Could Tylenol, in some cases, help ease that development? It's at least worth thinking about.