@janflute not a single human has gotten cancer (sarcoma) from Forteo. So it has been deemed safe to extend treatment. The more pertinent question, I think, might be whether it is still working to grow bone (Tymlos may have stopped building bone for me before 18 months, according to bone markers) or whether it is at least maintaining bone density/quality. I continued on Tymlos for the full two years regardless of those bone marker tests, and both my doctors suggested that it might still be of benefit. I am not sure that there are enough studies on this as yet.

Some of us are doing the two years, then a bisphosphonate to "lock in" gains, and then hope to do a bone builder again later.