Osteopathy is unregulated, meaning there is no government sanctioned college. However, there are two associations that in effect, act as regulatory colleges and only cover treatments from practitioners who belong to the OOA or the OAO. To belong to one of those, practitioners are required to have successfully completed competencies in the practice that are in line with WHO recommendations in terms of other regulated health professionals. There are many therapists that offer osteopathy, but some do not belong to these associations. Because of the lack of regulation, it is important to choose your practitioner carefully.
That said, the practice of osteopathy is a gently and non-invasive one, and though there are risks with any form of manual therapy, osteopathic practitioners are trained to use risk assessment and risk management when needed. Generally, treatments are not painful and relatively low-risk.