While I don't believe there is enough hard evidence to state any side effects that may exist, from the appearance of the anecdotal feedback that has been provided by users, there doesn't seem to be much in terms of sides. No gyno, as it has no effect on estrogen/androgen balance, and no suppression (as it is not an exogenous hormone source).
As for the joint tendon issues mentioned in previous post, I would consider that a secondary side effect of the muscle acquisition (most will see this side effect when rapid muscle gain is achieved), but not a direct result of administration.
None except 6lbs of muscle I have kept on after 1 run after being the same weight for a long time. Zero sides except some hunger but not sure if that is placebo. Love it second to GH.