Hm, how do you react to coffee? May sound lame but it does help with focus, for a lot of people. I've also tried L-theanine which is over the counter, was okay.
What type of games are you playing? I've been playing all types of video games since the 90s. Some have particular mindsets that could be helpful / a creative way to conceptualize the goal of the game to hone in on the objective.