What do you suggest if my uncle has recently been prescribed thc capsules insead of opiods. its basically synthetic weed. is it safe?

Probably marinol: and it is generally safe and well-tolerated. The person to ask these questions, who would know your uncle's full health history (without which nobody can give you any kind of accurate advice), is the prescribing doctor or the dispensing pharmacist. Your uncle needs to be asking the questions or signing a release so that you can get the information.