The Japanese word for medicine is
薬

くすり - kusuri

Japanese Definition

薬
1. n. A medicine or drug.
2. n. Usage: Only used in compounds.
3. n. A substance with mystical properties, especially one that has an effect on the body, health, or lifespan.
4. n. A medicine or drug, a pharmaceutical.
5. n. A chemical, generally toxic and used for its effect on living organisms, such as insecticide or herbicide.
6. n. A substance that has a beneficial effect in improving or maintaining one's health.
7. n. (figurative) Something that has a beneficial effect in correcting one's mistakes.
8. n. Gunpowder (from the “mystical substance” sense, and the second character in the word 火薬).
9. n. (figurative) A small bribe.
10. n. Usage: The medicine sense is probably the most common in modern Japanese.
11. n. (slang) A medicine or drug, especially a narcotic or other recreational drug.
12. n. Usage: The slang meaning is generally limited to when the term yaku is used as a standalone noun. In compounds, yaku refers more generally to pharmaceuticals, or sometimes chemicals.