It signals the pituitary gland to produce more human growth hormone. It can increase HGH levels to about the equivalent of 2 - 4 iu's. Recovery from workouts is greatly improved, it gives a fuller look to muscles, increases weight (mostly water), increases energy, and gives deeper sleep.
Negative side effects are mostly only noticed in the first weeks until the body gets used to it. This includes water retention, increased appetite, lethargy and a bit of a sinusitis type feeling. Deep sleep is one of the positive side effects and this gets a bit less but still remains throughout.
There is also no de-sensitization. Studies in humans have gone continually for 2 years without problems.
However, one thing to watch out for is insulin sensitivity and higher blood sugar levels but this can be largely negated with supplements like alpha lipoic acid together with curcumin.
Also, it is recommended to start with only 5 mg and going up gradually to 20-25 mg's. 10 mg's alone will give roughly the same HGH levels but going over 10 mg's will start increasing IGF-1 levels more.
It would have to be used for several months to truly benefit from it.