食たべてはいけません／だめです。
You must not eat it. (You can't eat it yet.)
飲のんじゃだめです／いけません。
You must not drink it. (You can't drink it yet.)

V-ては／ V-ちゃいけません／だめです: Used when talking about rules or manners on what you must/should not do and stopping someone from doing something that isn't appropriate.

Structure

A) このごはん、なべに入いれてもいいですか。
B) いいえ、まだ入いれてはだめですよ。
A) Can I put the rice in to the nabe pot?
B) No, you can't put it in yet.
なべのふたはまだとっちゃだめです。
You can't take the lid off the nabe pot yet.
かんこくでは食事しょくじのとき、茶ちゃわんを持もってはだめです。
In Korea, you mustn't hold the rice bowl during the meal.
車くるまをうんてんする人ひとは、お酒さけを飲のんではいけません。
People driving a car must not drink alcohol.

The phrase 「Ｖ-てはいけません」is less casual than 「Ｖ-ちゃだめです」.Used when writing or when giving advice, etc.