Dear Navi,

You wrote:

1-They did not know if SOME of those medications would have a positive effect on the patient.

2-They did not know if CERTAIN of those medications would have a positive effect on the patient.

Can’t these sentences mean two things:

a-As regards some of the medications, they did not know if they would have a positive effect on the patient.

b-They did not know if ANY of the medications would have a positive effect on the patient.

There is really no difference among any of the 4 sentences. Usually CERTAIN would be used if the speakers or writers were expecting specific medications to have the effects, but the overall meaning is the same. “As regards” is considered stilted. It is understandable but needlessly wordy and not commonly used. Just say “Regarding” or “Concerning.”