The supplement 5-hydroxytryptophan, 5-HTP, provides temporary relief of fibromyalgia, depression and insomnia. This over-the-counter product is a metabolite of tryptophan and building block for serotonin. Both of the latter substances play a role in controlling diet, and people often take 5-HTP to suppress appetite as well. The amino acid remains safe during long-term administration, but it may cause a short-term reaction. People should, therefore, speak to a doctor before using 5-HTP.
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Taking 5-HTP causes physical changes in the body. It also, however, causes psychological changes. A 2010 study in "Human Psychopharmacology" assessed the effect of 5-HTP on human behavior. Participants received either the supplement or a placebo before simulated gambling. Subjects given 5-HTP performed worse than those given placebo. Yet, these group differences decreased as the gambling risk increased. The latter finding suggests that the mental impact of 5-HTP can be overridden with enhanced focus.
Oral intake of 5-HTP may also cause feelings of nausea. A 2008 experiment described in the "Journal of Pharmacology" looked at the possible diagnostic use of 5-HTP. The supplement, for example, enhances positron emission topography, or PET, scans during screens for endocrine tumors. The authors administered either 5-HTP or placebo to patients during a single testing session. Smaller doses were well-tolerated, but doses greater than 100 mg forced some subjects to withdrawal from the study. In fact, a 300 mg dose of 5-HTP produced a 45 percent attrition rate. Interestingly, concurrent intake of the anti-nausea drug granisetron greatly reduced attrition.
Diagnostic use of 5-HTP has revealed other potential side effects as well. A 2010 report in "Progress in Neuro-Psychopharmacology & Biological Psychiatry" tested the impact of 5-HTP on hormone levels during magnetic resonance spectroscopy, or MRS, scans. Subjects received either 5-HTP or placebo during a single diagnostic test. They returned to the lab on another day and received the opposite treatment. Relative to placebo, 5-HTP decreased glutamate levels. This neurotransmitter plays a role in learning, and schizophrenics often show glutamate deficiencies. Substances which suppress glutamate should therefore be avoided.
Combining medications raises the possibility of drug interactions. Using 5-HTP also presents this problem. A 2010 article in "European Journal of Pharmaceutical Sciences" evaluated the concurrent intake of 5-HTP and gaboxadol. The latter drug remains under investigation as a potential hypnotic, and it shares binding sites with 5-HTP in the brain. In the study, rats were given either the drug combination or gaboxadol alone on separate one-day testing sessions. Results indicated that 5-HTP slowed both absorption and elimination of the sleeping pill. The supplement may interact with other prescription drugs as well. Thus, scientists must conduct additional tests before people can safely use 5-HTP.