YOU SAID:
"Please come when the medicine runs out."
INTO JAPANESE
「薬が切れたら来てください。」
BACK INTO ENGLISH
"Come back when the medicine wears off."
INTO JAPANESE
「薬が効かなくなったらまた来てください。」
BACK INTO ENGLISH
"Come back when the medicine stops working."
INTO JAPANESE
「薬が効かなくなったらまた来てください。」
BACK INTO ENGLISH
"Come back when the medicine stops working."
That didn't even make that much sense in English.