You can do this at home, except for the little inconvenience that growth hormone is a scheduled drug. I wonder what the results would be with just growth hormone. Let's ask Sylvester Stallone[1] who looks great for 75 and got caught trying to get into Australia with illicit Growth Hormone a while ago[2].
According to that paper it doesn't have a significant effect on the performance during exercise but it has a large effect on the serum level of GH. However it should be noted that this experiment was conducted on young healthy men and I have no idea if Niacin have the same effect in women or older men.
Growth hormone can be injected subcutaneously. They now come in convenient pens with adjustable dosage that are so fine you can't feel the prick. But yes, they must remain refrigerated.
[1]https://en.wikipedia.org/wiki/Sylvester_Stallone
[2]https://abcnews.go.com/Health/ActiveAging/story?id=3176015