Complex sentence: Those who use lithium should receive regular serum level tests and should monitor thyroid and kidney function for abnormalities, as it interferes with the regulation of sodium and water levels in the body, and can cause dehydration.
Split into simpler sentences: Those who use lithium should receive regular serum level tests and should monitor thyroid and kidney function for abnormalities. As it interferes with the regulation of sodium and water levels in the body, lithium can cause dehydration.