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In page 4-Methylthioamphetamine:

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Today the knowledge about the effects of 4-MTA is narrow, because of very limited research and experimental data. The only 4 studies that are conducted show a weak effect on dopamine and noradrenaline. This study was executed with a single dose of 4-MTA, no study where the effect of multiple doses 4-MTA where researched exist up to date.