Wow, that would be cool if it worked, but a little scarey sounding, what with it messing with body chemistry like that...I just googled it and found this:
Tyrosine, also called L Tyrosine, is not an essential amino acid since tyrosine can be made from the amino acid phenylalanine. Tyrosine is converted into dopamine and norepinephrine. Supplementation with both tyrosine and phenylalanine leads to alertness and mental arousal. Mind Power Rx with tyrosine works in a smooth, effective way, to increase alertness and focus, along with mood.
Phenylalanine and tyrosine are sometimes prescribed as antidepressants, usually in combination with other nutrients and herbs that have mood elevating properties. Some doctors also recommend these amino acids for appetite control.
Doesn't sound like it has much to do with tanning but what do i know...