From what I understand, there's a substantial body of research indicating that a slight suppression of the prefrontal cortex can reduce the sorts of inhibitive filters that constrain creative thought. Too much, obviously, and you impair your cognitive ability. Too little, and self-doubt and over-analysis rules.

Anecdotally, I've noticed that I'm significantly more fluent in my third language when I've had a drink or two. I get many, many more compliments. When I'm totally sober, I tend to trip up more and overthink the grammar.

There are lots of ways to reduce a hyperactive prefrontal cortex, including training (practicing art, meditating, etc.), but alcohol is by far the cheapest, quickest, and easiest.