Amino acid supplements are generally sold as sports supplements, and most are not very effective for that purpose as long as protein intake is adequate. Two of them, however, have piqued interest as a possible treatment for depression and other brain disorders. The science is not yet conclusive enough to recommend the combination of 5-HTP and L-tyrosine either as adjunct or sole treatment, and there are possible side effects, but people with depression should keep an eye on the progress of this promising line of research.
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Both 5-HTP and L-tyrosine work in the brain in ways that may enhance established treatments for certain brain-based conditions. L-tyrosine is a main ingredient of dopamine, epinephrine and norepinephrine, and 5-HTP triggers increased serotonin production. Serotonin is one of the main chemicals that produce feelings of happiness and well-being in the brain, and also helps regulate the appetite and control moods and sleep patterns. Dopamine, epinephrine and norepinephrine are chemicals called catecholamines that are responsible for the fight-or-flight response triggered by immediate danger or central nervous system stimulation. Low catecholamine levels have been linked to depression.
According to the University of Maryland Medical Center, L-tyrosine's connection to the catecholamines made it an easy choice for study relating to depression. Studies found that it may improve focus and memory during mental stress, but despite the fact that depression is linked with low tyrosine levels, tyrosine supplementation did not affect depression. In a similar fashion, 5-HTP's serotonin increase has been studied in relation to depression, and although the evidence is not yet conclusive, some research has shown it to be more effective than some prescription drugs. While the two supplements have produced equivocal results on their own, the combination of the two has shown promise in treating conditions other than depression.
A 2011 case study in the "International Journal of General Medicine" sought to reduce the negative side effects of the Parkinson's medication L-dopa, allowing patients to use larger, more effective doses. Researchers found that by administering a supplement containing 5-HTP, L-tyrosine and a sulfur amino acid with the L-dopa, side effects like involuntary movement, nausea and psychiatric symptoms do not occur, or are at least manageable because the supplement replaced chemicals that the L-dopa depleted or inhibited. A 2010 case study in the journal "Clinical and Experimental Gastroenterology" found that supplementing with 5-HTP and L-tyrosine helped a Crohn's disease patient experience remission once the proper serotonin levels were achieved. Of course, these examples are only case studies, not treatment plans, so more research is needed before the 5-HTP/L-tyrosine combo becomes a commonplace treatment for any condition.
As encouraging as the partnership between these two chemicals may seem at this point, they come with some risk. L-tyrosine can trigger migraines and increase thyroid hormone production, and may increase the risk of blood-pressure-related complications in people taking MAOIs. At this time, UMMC recommends that people taking MAOIs or L-dopa refrain from taking L-tyrosine. Pregnant or breastfeeding women should not take 5-HTP, which can also cause seizures in those with Down syndrome. Typical 5-HTP side effects include drowsiness, heartburn, nausea, diarrhea and vomiting. The supplement should not be taken with MAOIs or other depression medication, or any medication that affects serotonin levels. It may also interact with St. John's Wort, SAMe, and L-tryptophan. To be safe, consult your doctor before using either of these supplements, separately or together.