The company studies were two years and tht ws the limit in the original warning about bone cancer. That warning has now been lifted from Forteo and Tymlos and Forteo is now approved for more than 2 years. But I was told Tymlos is less effective after 18 months (or even one year) , I was told. I am doing the full two years but at this point it is just to maintain while deciding on next steps. My doc usually stops it at 18 months!