To be clear, some doctors and researchers have stated that they feel deer antler spray is unlikely to cause any significant benefits. This is because it only provides very small amounts of IGF-1, some of which may not even be fully absorbed. However, studies do show that higher doses, or using very high-quality supplements, may contribute to some improvements in performance, body composition, etc. IGF-1 itself has been studied extensively. It can certainly change the way the body looks and operates. Whether or not the role of IGF-1 in the body will translate into any real benefits when obtained from deer antler products will depend on the specific person and dosage used.
A systemic review on human interventions makes note of a study conducted on patients of osteoarthritis (Edelman et al. 2000; cannot be located online) which found improvements in joint pain symptoms relative to baseline in the Velvet Antler group and not placebo, although a lack of information on blinding and randomization precludes results that can be drawn from this study.