What negative effects of human growth hormone are there?

All of them: There are no positive effects. Growth hormone in adults that don't need it can lead to diabetes, pancreatitis, skeletal pain, headache, gynecomastia and a host of medical problems. Plus it's very expensive, requires daily injections, isn't covered by your insurance, and would probably have to be obtained on the black market, so who knows what you'e be injecting?