Human Growth Hormone. It helps rejuvente people in appropriate amounts ( too much is not good for you either).
Most effective taken by injection, but aside from requiring a prescription, it is also very expensive. There are some claims, that by taking certain supplements, you can stimulate your body to make it, but I am personally skeptical about that.
I don't know whether sublingual HGH is really HGH or not, but it's interesting that it produces good results, according to a personal testimony here.
(But anyone considering HGH should check with their doctor, for example, people with diabetes or glucose tolerance problems should not take it, because HGH makes it worse)
For others it is supposed to be helpful in giving more energy, help muscle tone, skin, etc.
But, repeat, anyone considering it should do serious research and check with the doctor, before doing so.