There aren't any. But that is not how Medical science works. You don't start taking drugs and then ask a scientist to show me a study that proves it doesn't work. I defer to the Hippocratic Oath here.
"None of the studies that have been released meet the gold standard for demonstrating a drug’s effectiveness – a large-scale, double-blinded randomized controlled trial (RCT), though multiple trials of that kind are under way."
One thing we do know from many years of usage is that it does have a lethal side affect of heart arrhythmia.
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