How to fix homebrew permissions?

I was able to solve the problem by using chown on the folder:

sudo chown -R "$USER":admin /usr/local

Also you'll (most probably) have to do the same on /Library/Caches/Homebrew:

sudo chown -R "$USER":admin /Library/Caches/Homebrew

Apparently I had used sudo before in a way that altered my folder permission on /usr/local, from here on forward all installations with brew have proven to be successful.

This answer comes courtesy of gitHub's homebrew issue tracker

https://stackoverflow.com/questions/16432071/how-to-fix-homebrew-permissions