People with Graves' disease, phenylketonuria, and hyperthyroidism may not be able to take L-tyrosine. Safety precautions also apply to people with certain allergies or sensitivities. In order to ensure your safety with L-tyrosine, make sure you look for a reputable supplement manufacturer that abides by the GMP rules and that the bottle carries the USP seal.
Is L-Tyrosine Safe?L-tyrosine (also known just as tyrosine) is a dietary supplement used to treat a variety of conditions. You may not be able to take L-tyrosine safely if you have:
- Hyperthyroidism (an overactive thyroid)
- Graves' disease
- Phenylketonuria (PKU)
- Any allergies, including allergies to food, dyes, or preservatives.
Also, let your healthcare provider know if you are:
- Pregnant or thinking of becoming pregnant
You should also be sure to tell your healthcare provider about all of the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements.
Specific L-Tyrosine Warnings and PrecautionsWarnings and precautions to be aware of concerning the safety of L-tyrosine include the following:
- L-tyrosine is used by the body to make thyroid hormones. Therefore, if you have high thyroid hormone levels (such as with hyperthyroidism or Graves' disease), you should not take L-tyrosine supplements without your healthcare provider's approval and supervision. L-tyrosine could make these conditions worse.
- L-tyrosine supplements can interact with some medications (see Drug Interactions With L-Tyrosine).
- If you have phenylketonuria (PKU), do not take L-tyrosine supplements unless your healthcare provider specifically recommends that you do so. It is important for people with PKU to closely monitor and balance their intake of amino acids, including L-tyrosine.
- If you decide to use supplements such as L-tyrosine, what you see on the label may not reflect what is in the bottle. For example, some herbal supplements have been found to be contaminated with heavy metals or prescription drugs, and some have been found to have much more or much less of the featured ingredient than their label states. Make sure the manufacturer of your L-tyrosine supplement is trusted and reputable. It is a good sign if a manufacturer abides by the rules of Good Manufacturing Practices (GMP) for drugs. It is also a good sign if a product has the United States Pharmacopoeia (USP) seal, which means that the product has been independently tested and shown to contain the correct ingredients in the amounts listed on the label. Your pharmacist is a good resource for information about which manufacturers are most reputable.
- It is not known if L-tyrosine supplements are safe for pregnant or breastfeeding women (see Tyrosine and Pregnancy and Tyrosine and Breastfeeding).