I take ritalin and I find I can overcome the loss of appetite by using products from Walden's farm. They make a whole range of completely calorie free sauces, dips, butters, etc. They even have calorie free pancake syrup, marshmallow dip, bbq sauce and peanut butter. But if you aren't worried about him picking up a bit of fat to bulk up for rugby then give him sauces and honey on his meals and oats and they'll be a lot easier to eat. Once he is on a proper diet for his stats he will no doubt start picking up weight. In my opinion, it is not worth him taking steroids at his age and level of sport. it's under 19 school rugby so their should be testing involved and it's not going to be his career so potentially risking his health is not necessary. In terms of the correct approach you have it spot on and are lucky to have that open relationship and of course it would be much better to do it properly if he's going to do it at all but I'd say get him to enjoy his food and he'll pick up the weight he wants to. 17 and taking steroids opens him up to a world he is definitely not yet ready for. hope this helps and goodluck.