With a DEA license to prescribe from schedule II - V, technically yes, we can write for anything on those schedules. Realistically though, it doesn't happen (at least much) because why would we want to? I have no desire to manage and take responsibility for someone's thyroid condition.
If we have a reason to use a drug we can do so. For example, I've written for anxiolytics before in the case of pre-operative acute anxiety but won't manage it long-term. I prescribe gabapentin before surgery as a part of multi-modal anesthesia even though it's an anti-epileptic drug and seemingly outside of scope.
I like Lifepod's phrase, "stay in your lane."