You can obtain some weight‐loss medications or aids in Australia that don’t require a full doctor’s prescription (for example pharmacist-only ones).
There are also many supplements and products marketed in pharmacies over the counter (OTC) for weight-loss- however these are very different from prescription medicines in terms of evidence of effectiveness and regulation.
The more proven, effective medications for weight management do require a prescription and careful monitoring.
OTC doesn’t mean “no risk” or “guaranteed effective”.
If you’re thinking about going down this path, it’s worth consulting a healthcare professional (doctor, pharmacist) to check suitability, safety and evidence.