I agree with all the posts that have been made on this. Growth Hormone (GH) and the closely associated IGF-1 (Insulin-like Growth Factor - 1), are pro-growth, pro-healing hormones. They are sort of opposite of Rapamycin in many ways. Rapamycin decreases mTORC1, slows protein synthesis, slows cell growth and lowers growth hormone levels (which is down stream in the molecular pathway).
All the lifespan research that has been done on GH/IGF1 (they usually go up and down together), indicates that higher levels over the life of the mammal, shortens their lifespan. See this thread for details on this: IGF-1 inhibitors and lifespan extension?
A new company, Loyal for Dogs, is coming out with a new drug that lowers Growth Hormone/IGF1 levels to improve healthspan and lifespan in large dogs. Its raised over $60 Million in funding, and the FDA has approved the protocol for validation of it working and the clinical trials are in process. Their goal is to eventually bring their drugs to human applications (in fact Celine H., the founder of Loyal, has told me that the FDA is requiring them to provide human data even for their dog FDA approval, because the FDA likely expects some people to also start taking the dog medication prior to any human clinical trial or approval).
https://www.businesswire.com/news/home/20231127326868/en/FDA-Agrees-Loyal-Data-Supports-Reasonable-Expectation-of-Effectiveness-for-Large-Dog-Lifespan-Extension
More news stories and information on Loyal for Dogs and their progress/press from past threads is here: Search results for 'Loyal dogs' - Rapamycin Longevity News
But - increased GH / IGF1 may be pro-health span and pro-healing if you are recovering from an injury, etc. But there have not been many papers on GH for healthspan and longevity (you might ask the “longevity clinic” you are talking to what research papers validate its use in longevity…). So the data is still pretty sparse in this area. Generally it was popular in the early days of “anti-aging medicine” because I think generally the results are that it makes you feel better and helps growth of muscle, etc. Similar in men to testosterone. But the longer term data is negative… I don’t think you want to be taking HGH for many years consistently, based on the lifespan data in animal studies.
Overall, the data in animals suggests a lifespan increase (and healthspan increase) of 15% to 30% for rapamycin.
The data suggests that higher GH levels (in animals, for their entire lifespan) are likely to shorten lifespans in animals by perhaps by 30% to 50% (animals with extremely low growth hormone levels - for example the Ames and Snell Dwarf mice) typically live up to 50% longer with their very low GH/IGF1 levels, compared to “wild type” (regular / normal) mice.