Son was caught taking prescription drugs from work and was charged with class 4 felony, what would be his punishment?

Don't have enough facts to determine that. What were the drugs, how much did he take? My advice, get an attorney.

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. A lot will depend on the drugs and the amount taken. I strongly suggest that you contact an experienced criminal defense attorney for a face-to-face consultation and give him/her all of the facts surrounding your son's case. He/she would then be in a better position to analyze his case and advise you of his options.

That's going to depend on a number of factors: history if prior offenses, age, any mitigating factors etc.

Anywhere from probation to prison depending on the exact charges and the circumstances.

This is a felony. Could be up to 20 years in jail. I suggest you consult with a criminal attorney.