Acetyl groups.

Who'd a thunk that something as simple as an acetyl group could be so useful?

Acetyl group on Wikipedia

A common substance which is mostly an acetyl group is acetic acid, the acid in vinegar. Vinegar has quite a few medical uses, as well as making fish & chips/fries taste great.

I was reading stuff on the internet (as you do ;-) ) when it occurred to me that several substances had acetyl groups in them, e.g. Aspirin (acetylsalicylic acid) , Paracetamol/Acetaminophen (N-acetyl-p-aminophenol), Heroin (diacetylmorphine), DCA (dichloroacetic acid), Acetylcholine, Acetyl-CoA, Acetylcysteine & Acetyl-L-carnitine.

Here's an amusing (unless you are/were an addict) snippet of information about Heroin (emphasis mine) from History:- "From 1898 through to 1910, diacetylmorphine was marketed under the trademark name Heroin as a non-addictive morphine substitute and cough suppressant." Oh, whoops!

Acetylation makes substances more active in the body & increases their ability to cross the blood-brain barrier, as well as having other functions in the body (e.g. changing the expression of proteins & genes).