Lithium dietary supplements usually contain lithium orotate, a different lithium “salt” from the lithium carbonate or lithium citrate in most prescription lithium. Lithium doses in dietary supplements are much lower than in prescription lithium—usually 10mg per pill instead of 300mg or 450mg. There are some claims that lithium orotate is better absorbed or more active, so lower doses are still effective. But there is no clear evidence (no randomized, placebo-controlled, blinded trials) showing that low doses of lithium orotate are effective for treatment or long-term prevention of mood symptoms.
Still, it is possible that very low doses of lithium are helpful for some people. Lithium is a naturally occurring mineral, and trace amounts are present in the water many of us drink. And areas with more lithium in the water supply tend to have lower suicide rates! So, very tiny amounts of lithium —less than 1% of the lithium even in low-dose dietary supplements—might sometimes be helpful.
But if you are taking prescription lithium, you definitely do not want to switch to a low-dose nutritional supplement without talking with your doctor. For some people, suddenly stopping lithium or suddenly decreasing the dose can cause severe mood swings or symptoms of mania.
And you wouldn’t want to add a lithium nutritional supplement to prescription lithium. That might increase your blood level of lithium enough to cause side effects or increase your risk of long-term problems from lithium.