The true form of synthetic human growth hormone is a prescription taken by injection. It was what most of the research was conducted on, and has been around for decades.
Most major pharmaceutical companies deliver synthetic human growth hormone as injections. It was originally developed for children with growing disorders that involved a lack of the human growth hormone, because their pituitary gland wasn't manufacturing as much as was required. And it still is the primary reason for it's existence today.
Then doctors started studying the effects on health and aging. The research was generally very impressive. But it wasn't going to be available to the general public for quite some time. At least legally. For a while, human growth hormone injections were illegal in the United States. If someone was intent on using it, they had to get it illegally from some other country. Now, it is legal. But if you are going to use human growth hormone injections, you will need a prescription, or go to an anti-aging specialist or clinic. Using it for "anti-aging" and longevity purposes was essentially a "side-effect" discovery, and is still in the realm of what is called "off label" usage.
HGH injections are usually given/taken on a daily basis, or several times a week. Some doctors will want you to come into the office or a clinic to get your injection every day. Others may prescribe self-administration, and teach you how to do it yourself. It is very similar to a diabetic giving themselves daily insulin injections, and in fact, uses the same fine, tiny needles/syringes. The invention of the human growth hormone injection "pen" has made self administration less complicated.
In the past, human growth hormone injections were the only way you could absorb human growth hormone. And it was very expensive. It can still cost between 4 or 5 hundred to thousands a month, depending on where you buy it, and if you have a clinic administer it and monitor your results.