If you want it enough, then you will do whatever you have to do to make it happen, and this includes standing up to your parents and telling them that your life is your life and that you don't want the future they have mapped out for you for your own good. You are the only person who is ever going to live your life. This does not advocate doing stupid things, like drinking or drugs. Learn from the mistakes of others in regards to stupid things. You don't have to experience them yourself to know they're dumb.
Writing is one hell of a hard way to make a living.
Don't go into it thinking that you're going to be rich, or famous. Only go into it if it is what you love to do, and if you're going to love it whether you make tons of money or a subsistence living while working a day job. On the other hand, medicine is one hell of a hard way to make a living, and with writing, at least, you're rarely exposed to fatal diseases. I don't find it easy to sit down and write. But I have no strategies.