Possible side effects of L-tyrosine include nausea, fatigue, heartburn, joint pain and headache, according to WebMD. L-tyrosine is considered generally safe for oral or transdermal application in doses of up to 150 milligrams per kilogram per day for up to three months.
The medical community does not have enough information on the effects of L-tyrosine on children to determine whether it is safe to use, states WebMD. Additionally, it is not known whether L-tyrosine is safe to use during pregnancy or while breast-feeding. Patients of depression, Parkinson's disease and attention deficit disorder use L-tyrosine to maintain mental alertness.
One important contraindication to the use of L-tyrosine is in conjunction with Graves disease, reports WebMD. Graves disease manifests itself through an overactive thyroid gland that uses L-tyrosine to produce thyroxine. Excess levels of L-tyrosine combined with hyperactivity of the thyroid gland can create conditions in which the body creates dangerous amounts of thyroxine, so individuals suffering from Graves disease should not take any L-tyrosine supplements.
Additionally, L-tyrosine is known to interact with levodopa, according to WebMD. L-tyrosine may reduce the effectiveness of levodopa by decreasing the amount of levodopa the body is able to absorb. As a result, medical professionals discourage the use of l-tyrosine and levodopa at the same time.