Creatine is not a drug, it's a food product. It is found naturally in all sorts of stuff, mainly red meat.
3g is an effective dose and is more than enough once your body's levels become saturated. Yes, you can take more to get there but what's the point. No, you don't need to "cycle off" either, not if you are taking 3g per day.
Like any product it can be misused. If your creatine levels are full, any extra in your blood stream is filtered out by the kidneys. That, over time, can cause serious stress on your kidneys, if you are taking some of the retarded amounts that some claim. e.g. 40g or more per day.
Now, here is the big secret for getting big. Ready? Don't tell anyone this cos it's obvious that the world of bodybuilding and such is full of dumb kuntz that have no idea about this big secret. Here we go. OK. Cough.
Eat. Lots. Eat lots of protein and healthy fats. Carbs area a waste of time, though they are fun and can make life more enjoyable. Have your nephew (I assume its a boy, even though you called him your neice then a "him") eat protein at every meal with some healthy fats (nuts, natural peanut butter, avocado, olive oil, fish oil, etc) plus something green. Minimum of 4 meals per day (students tend to get a bit busy) or 6 is better. So a typical meal will be eggs/chicken/beef/lamb/fish etc with some oil or nuts and such.
Add to every meal something green. Salad, spinach, broccoli.
Now, if he only eats that he will grow like a weed without feeling stuffed. However, if AFTER he eats a typical meal he feels like something more, he can eat carbs, but not if they stuff him so much he has trouble eating his next meal. Like I said, they are only entertainment. There are no essential carbs, but there are essential amino acids (protein) and fats.
Now, you are battling a huge juggernaut with the supps industry, and supps can help a lot. But it's best that he sorts his diet out so that he can then supplement with what he needs. Creatine will be one of those items. Go check out Bulk Nutrients, one of the sponsors here. They have very high quality product without fillers and chit and will not rip you off.
Now, some here, and elsewhere, may get a bit pissy with the above "secret" but bottom line is that muscle is made from amino acids and fat, not carbs. Just make sure he gets his building blocks in (protein and fat) and then he can eat anything he wants on top of that. ice cream, pop tarts, pizza, whatever. Go for it. At his age his growth will be directly proportional to what and how much he eats. More is better. As long as he gets his protein, fat and greens in first.
It's that simple. At that age his hormones are belting around like a train out of control. Add in some decent weight training and every gram he eats will turn into bone, sinew, muscle and blood. He will grow before your eyes.
Live long, get big, and prosper.
