Gabapentin did not meet FDA standards to be labeled as a drug to treat anxiety/depression/BP, but that doesn't mean that it can't be used off-label.

Many pdocs and other physicians prescribe meds off-label when there is broad evidence, somewhat of a consensus among them, that the meds may be effective in treating disorders the FDA hasn't approved them for.

All meds have side effects no matter why you're taking them. For some conditions, you may need more monitoring tho.