Phentermine is often prescribed for short term use to cause weight loss for people who are obese.  However, some studies have shown that in combination with some other drugs it can cause serious heart problems.   Remember this is for SHORT TERM use, so please discuss with your doctor the length of time that you will be using the Phentermine.    Some doctors prescribe Topomax with the Phentermine in very specific doses because it can cause weight loss, but most people take Topomax for migraine headaches.  Phentermine can cause Migraines so it seems as if you are going in circles, but some people can take one or both of these medications without a problem.  Make sure you talk to your doctor if you have rapid heart beat, or any other debilitating side-effects.  Also, keep track of any symptoms you may have that make you feel not quite yourself.