To be fair CAS and IAAF disadvantage Caster Semenya

It comes as the World Medical Association slammed the IAAF's regulations to limit testosterone levels in female athletes labelling them "unethical" and "flagrant discrimination".

CAS ruled the IAAF's regulations were needed to ensure fair competition in female events ranging from 400-metres to 1600m, despite also finding them discriminatory on Wednesday.

It means if two-time Olympic gold medallist Semenya wants to compete at the world championships in Doha in September then she has to start taking medication to lower her testosterone levels within one week.

But Canberra transgender handballer Hannah Mouncey says the drugs used can't lower testosterone to within a desired range. Instead, it would effectively wipe it out of her system to undetectable levels.

That means the testosterone levels of Semenya, and other athletes like her, would now be well below that of other female athletes they competed against.

Given the IAAF's regulations were being implemented on the premise that testosterone improves performance that means the South African runner would be severely disadvantaged.

Mouncey said she was surprised by the decision given the study the IAAF used to back up their regulations had been widely criticised and discredited.

"For people in her position they should just be allowed to compete because it's naturally occurring," she said. "She basically just got lucky. She's not the only person in the world with her condition yet she's the only one who is as successful as she is.

"How much of it is hard work? It sells her short too, saying the only reason she's successful is this. No one else has been.

"Where it's actually putting her now is behind the athletes she is competing against, because they will have significantly more testosterone than her."

The WMA called on physician's to boycott implementing the IAAF's regulations and said they contravened international medical ethics and human rights standards.

WMA president Leonid Eidelman said the regulations were based on "weak evidence from a single study".

"They are also contrary to a number of key WMA ethical statements and declarations, and as such we are calling for their immediate withdrawal," he said.

However, Mouncey said CAS's ruling could help transgender athletes' cause.

They're already forced to take testosterone medication. Mouncey's own levels have been reduced to effectively zero.

"The research they're putting up against her actually supports the inclusion of trans athletes because it's showing the suppression of testosterone makes a huge difference," she said. "They may have won that battle, but they have supported trans athletes more in doing so."