Praise be to Allaah.
Now is the appropriate time for you to be thinking of your future, for this will lead you to take decisive action from now. If you know for sure that you can avoid selling everything that is forbidden in sharee'ah, then there is nothing wrong with continuing your studies. But if you know that you will not be able to avoid it, or you believe it is more likely that you will be too weak to avoid it, then you should change to another specialty from now, so that you will be able to practice a profession that will be acceptable to Allaah. Alternatively, if you see that there are impediments to practicing your specialty due to the involvement of forbidden items, you could take the initiative and commitment to finding permissible alternatives, whether natural or synthetic, to the forbidden items. The important thing is to ensure you will not put yourself in a position where you are involved in the sale, receiving, or giving of items that are haraam.
Some of the issues having to do with medicine need to be contemplated; for example, if a medicine contains alcohol and would intoxicate a person if a large amount was drunk (i.e. of the medicine itself), then it is haraam; otherwise it is not haraam. Similarly there are questions surrounding the impurities that form the ingredients of some medicines: is the structure of the impure substance changed in totality when it is mixed with the other ingredients, or does it remain the same? Surely you are not unaware that there are medicines taken from the urine of pregnant women, or blood, or from body parts removed from humans, such as placentas, to which the rulings concerning dead meat apply. The rulings governing all of these things need to be investigated, and consequently the rulings regarding their sale; the matter needs to be studied both from the point of view of Islamic Sharee'ah and of chemical analysis.
And Allaah knows best.