Using a single amino acid supplement may lead to negative nitrogen balance. This can lessen how well your metabolism works. It can make your kidneys work harder. In children, single amino acid supplements may cause growth problems.
You should not take high doses of single amino acids for long periods of time.
Very high doses of leucine may cause low blood sugar (hypoglycemia). It may also cause pellagra. Symptoms of this can include skin lesions, hair loss, and gastrointestinal problems.
People who are pregnant or breastfeeding shouldn't use leucine supplements. People who have maple syrup urine disease), a rare inherited defect of metabolism, shouldn't take it either. They also shouldn't take the other branched-chain amino acids, such as isoleucine and valine.