I'm finding it hard to decide what course I want to do however i've narrowed it down to either chemistry or pharmacy. Would it be difficult to write a personal statement tailored to both or would it decrease my chances of getting into either courses.
I would say focus on one subject. Theoretically it's possible to write a good personal statement for both, but very difficult and I wouldn't recommend it. What are you planning on doing with your degree/post-degree? Thinking about that question will be useful for choosing between the subjects if you decide to do that.