Learn Italian: La droga rende le persone deboli.

When "make" means "to cause someone or something to become a certain way" and is followed by an adjective (like "weak", "happy", or "crazy"), Italian uses rendere. You use fare when "make" is followed by a verb, as in making someone do an action (the causative fare).

Could I say La droga fa le persone deboli?

No, that is a direct translation from English that sounds very unnatural in Italian. Fare doesn't work directly with adjectives to express a change of state. You must use rendere + adjective. If you really wanted to use fare, you'd have to use a verb instead, like fa indebolire le persone (makes people weaken).

Why is La droga singular here when the English translation says "Drugs"?

In Italian, a broad category or phenomenon is often expressed in the singular with a definite article. While you can say le droghe to refer to distinct types of drugs, la droga is the most natural way to talk about narcotics as a general concept or societal issue.

Why does deboli end in "-i"?

Because it is an adjective modifying le persone (feminine plural). Remember that adjectives ending in -e in the singular (like debole) change to -i in the plural, regardless of gender. The adjective must agree with the object whose state is being changed.