It is quite untrue that synthetic hormones are no different from natural hormones. When women are given HRT or the contraceptive pill the hormones in them are synthetic: ethinyloestradiol, a chemical oestrogen, and a progestogen. There is now considerable evidence that these hormones increase many health risks.
The natural or bio-identical hormones have a chemical structure that is identical to the hormones made by the body so that when these natural hormones are used they do not have the same health risks as the chemical hormones. This is because the body recognises them and has pathways for dealing with them as it would the hormones naturally produced by the body. As a result they do not accumulate in the body and cause problems.