@janflute it might be best if you could find study data comparing the generic vs forteo. Anecdotal accounts may offer comfort to your mind, but may not be reproducible due to individual variation.

Formulation like tablets have binders, fillers and outside coatings. When a generic is made, while the active ingredients would and should be the same, the remaining inactive ingredients may not. This might cause variations in tablets’ disintegrating rate and in turn affecting rate or extend of absorption and max blood concentration etc. This is why there are people insisting to have a particular generic brand of a, say blood pressure med (because the effects are very noticeable) instead of another, although they are the same or have the same active ingredient.

Biologics like teriparatide/forteo are made from recombinant technology, there is no need to doubt their active ingredient. The differences might be in carrier media, delivery pen, as well as the usage of preservatives, if any. There sure were clinical trials before a generic is approved by FDA. If trial data were not available, you can check the generic rating. If it’s ab rated (rating always includes efficacy), personally I wouldn’t worry too much.