Thank you for your question. Most of the major studies conducted have followed patients for 2 years, though there is evidence that it's safe for up to four years. That being said, there is no direct answer to your question. This medication hasn't been on the market long enough for there to be long term studies of more than just a few years. This is something that you would have to discuss with your doctor to determine how long you should continue to take the medication. If it's still providing benefit to you and you're not experiencing any negative effects, it may be in your best interest to keep taking it.   Best of luck, Casey