Also rickrock did suggest an 8 week primo run here:
http://www.elitefitness.com/forum/showthread.php?p=17770703
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I personally don't see a problem with 8 weeks if you don't abuse the dose (keep it at 3 caps max) and run N2guard the whole time. I'm running Primoboldex right now, and the gains are great but the sides for me have been minimal