Intramuscular testosterone undecanoate is available in the United States , Canada , Europe , and elsewhere in the world.    It is approved in over 100 countries worldwide.   Oral testosterone undecanoate is available in Canada, Europe, Mexico, Asia, and elsewhere but not in the United States.   Intramuscular testosterone undecanoate is marketed most commonly as Nebido in Canada and Europe and as Aveed in the United States while oral testosterone undecanoate is marketed most commonly as Andriol.   
I have taken Nugenix for about 3 years. I swear by it. When I was about 60 my testosterone levels had dropped to about 50T before I did anything about it. I was extremely depressed almost incapable of doing my job. I am a professional in an office responsible for about 150 clients.
My first doctor gave me a T gel that I rubbed in. My second doctor began a testosterone injection regimen 200 mg every two weeks. Believe it or not that did return me to active sexual activity. It wasn’t until I started to take a similar product at GNC that put the hard back in an erection. After starting the injections I could get a limp erection but I could not perform. I could do my job and the injections put a swagger back into my step. Nugenix was the break over point for me. That is my experience without using any medical language.
Testosterone is a hormone produced in the male testes. During a boy's pubescent years (ages 9 to 14), there is an increase in production that leads to male secondary sexual characteristics such as a deeper voice, more muscle mass, facial hair growth and enlargement of the Adam's apple (among others). Some teenage boys experience these puberty changes at later ages than others. The timing of puberty is often genetically determined (through heredity), but other factors can play a role in delaying it, such as poor nutrition, physical trauma and certain diseases. Stimulating testosterone production naturally is possible in teen boys, although in rare cases hormone therapy may be needed to trigger and complete puberty.