After that qualified reassurance we read that "In recent years, large-scale epidemiological studies have convincingly shown that lithium treatment elevates the risk of chronic kidney disease and renal failure."
And further, "Other patients may be able to switch to a different mood stabilizer medication, but kidney function may continue to deteriorate even after lithium cessation. Most, but not all, evidence today recommends using a lower lithium plasma level target for long-term maintenance and thereby reducing risks of severe nephrotoxicity."
The risk of nonreversible kidney damage seems to counter your claim that "lithium can be safely prescribed over a protracted period of time". Even careful monitoring isn't sufficient since detecting these kidney problems does not guarantee they can be corrected ("may continue to deteriorate even after lithium cessation".) Thus a more accurate formulation would be "lithium can be safely prescribed over a protracted period of time... as long as you're lucky enough not to incur this dangerous side effect." Or possibly, "lithium can be safely prescribed over a protracted period of time when it is administered in low doses."
