Do students on a NON-MIGRANT O "ED" visa need a medical certificate for specific diseases in Thailand?

Okay, now that we know what's what;

The O/P has an ED visa issued already from a thai consulate in the US based on attending a Thai university.

They were only asking about the medical certificate (which is required for O-A and some Non-B visas) not anything else. SO the answer is NO, if you have the ED visa inked into your passport already and you meet the other criteria to request entry to the country you do NOT need a paper saying you don't have those diseases.