Something that is drastic is violent, forceful, and extreme. If you are saving for a car and you only have $50, you need to make a drastic change to your money accumulation scheme.
The word drastic comes from the Greek word for effective, but we use it to mean incredibly effective. If you want a drastic makeover, get rid of all your clothes, change your hair completely, and pick up a new way of speaking. Sometimes drastic action goes too far and so has bad consequences. A bankrupt company might make a drastic decision to fire the management without figuring out how to manage itself in the future.