You shouldn’t lose or gain weight as a side effect of taking Forteo. Weight changes weren’t reported in people taking the drug in clinical studies.
But it’s possible that weight loss can occur due to a higher calcium level in your blood, a less common side effect of Forteo. Symptoms of having an increased calcium level can include nausea, vomiting, constipation, fatigue (low energy), and muscle weakness. It’s possible that these symptoms can lead to some weight loss.
If you notice these symptoms or weight changes while using Forteo, talk with your doctor. They may check your calcium level with a blood test.