How do growth hormones affect the size of commercial chicken eggs?

No and they are not used in most countries. Growth hormones are banned in all of North America and most of Europe. It is just not feasible to inject a drug into a chicken. Growth hormone injections are worth more than the chicken. Hormones cannot be fed to the birds, it does not work, they have to be individually injected and a current cost of about 3.00 US. A chicken, dressed out and sold to a vendor for resale nets a producer about 4.50 US.