[ekianjo]

> Japan, China, South Korea for example does their own drug testing and development so would they find that a particular drug doesn't work on their population at all?

Yes, it happens sometimes that certains drugs approved in the US fail to make it in Japanese clinical trials. Recent one I can think of is Prozac:

https://clinicaltrials.gov/ct2/show/NCT01808612

It did not show to be better than Placebo in the Phase3 Japan trial. (https://clinicaltrials.gov/ct2/show/results/NCT01808612?sect...)

There could be multiple reasons for that, but in the end the drug is not approved in Japan.