Stress fractures (SFX) are a major problem for athletes, because they need to be a relatively long period of time away from activity. Most SFX are treated conservatively, and in some cases may result in delayed union or nonunion. To date, there is not any medication approved to accelerate the healing of SFX. Recently, teriparatide, an anabolic agent used in the treatment of osteoporosis, has shown as a promising treatment to accelerate the healing of fractures, by increasing bone formation. Objectives: To evaluate the efficacy and safety of 20 μg and 40 μg of teriparatide compared with placebo, for treating lower extremity SFX in high-level and high-performance athletes. Efficacy endpoints will be the time to radiographic healing and the return to sport time, measured in weeksDesign: A phase IV/II, multicenter, randomized, double-blind, placebo-controlled clinical trialSetting: Hospital Universitari Doctor Josep Trueta and five Sports Medicine Centers of CatalunyaParticipants: High-level and high-performance athletes diagnosed with lower extremity stress fractures. Intervention: Teriparatide 20 μg (n=46), teriparatide 40 μg (n=46) and placebo (n=46), all as a daily subcutaneous injection for 8 weeks