I don't know if it's the same for international student but home students are generally expected to have studied chemistry between 16 and 18 as A-levels (as well as biology to a lesser extent). If you haven't studied those or an equal qualification to a level it might make it difficult for you to get into normal medicine and you might have to look into medicine with a foundation year, although you'll meed superb stats because it's much more competitive than normal entry medicine