You don't have to,
but it's HIGHLY recommended.
The Big Bang Theory Season 3, Episode 2
Me, a HIGHLY
regarded physicist.
The Big Bang Theory Season 5, Episode 6
I HIGHLY doubt that.
The Big Bang Theory Season 1, Episode 10
Highly unethical for an astrophysicist.
The Big Bang Theory Season 3, Episode 4
He always spoke HIGHLY of you.
Game of Thrones Season 6, Episode 8