The IGF-1 found in deer antler spray is derived from deer antler velvet, the tissue found inside the deer's antlers before they fully harden. Since deer antlers grow incredibly fast, it is not surprising that the horns are rich in IGF-1. This is a naturally-occurring form of IGF-1, meaning it is not made in a lab. As a result, deer antler velvet is considered a dietary supplement by the Food and Drug Administration, and unlike synthesized drugs, the product does have to be proven safe or effective before it's sold to the public.
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.