"I need some medicine" => (literally) 나는 약이 (좀) 필요해. In real life, people are more likely to say it like this: - 나 약 좀 먹어야겠어. (약 좀 사다[찾아] 줘) => I have to take some medicine. (Please go get[find] it for me) - 나 약 먹어야 되려나 봐. (사다 줄 수 있겠어?) => It looks like I'll have to take a medicine. (Can you go get some for me?)