Dec. 21 (HealthDay News) -- Too high a dose of lithium and other drugs that inhibit an enzyme called GSK-3 beta can impair, rather than improve, neurological function in patients with Alzheimer's disease and should be used with caution, a new study says.

Lithium is currently undergoing clinical trials as a treatment for Alzheimer's disease. It has been shown to be safe in treating people with manic depressive illness.

"People might think that if you make the inhibitor stronger and stronger, that would be better. Our in-vitro experiments show that you will have to be careful with how you use GSK-3 beta inhibitors, because if you use too much, it will interfere with and possibly kill neurons," study co-author Dr. William D. Snider, professor of neurology, cell and molecular physiology at the University of North Carolina at Chapel Hill's School of Medicine, said in a prepared statement.

He and his colleagues were surprised by the findings of their study -- which used mouse neurons in cell culture -- because previous research has shown that certain doses of GSK-3 beta inhibitors improve neuronal function. The findings were published online Dec. 21 in the journal Neuron.

"It's known that when GSK-3 beta is inactivated, that tends to allow the processes inside the cell it regulates to function normally," Snider said.

The study, conducted by American, Canadian, and Japanese scientists, was funded by the U.S. National Institute of Neurological Disorders and Stroke.