"Obat ini akan memperkuat tubuhmu."
Translation:This medicine will strengthen your body.
You're right. That's what "memper-" do. But only when "memper- + adjectives", remember that "memper-" is also mixed with some other endings to form other words which then form different meanings than this one. Like, "memper-(word)-kan" for example, "mempertanyakan" (memper-tanya (ask/question)-kan) means "to question". So yes you're right but as long as the "memper-" is not mixed with other endings.