Nothing, but headache medicine is not good for your liver so I wouldn't suggest doing it more than you have to.I suggest you Natural remedies for headaches through this you get instant of knowledge about How do you get rid of a headache ?
Usually nothing happens in such cases. But you should know about side effects and contraindications before taking any pill. You can check this info online. Here I can suggest visiting Canadian Pharmacy Online as this site can provide you with the description of necessary medication.