So its made by a process called recombinant DNA technology.
Recombinant DNA (rDNA) is when genes or DNA is inserted into the DNA of a microorganism (like a bacteria) and the microrgaism uses this gene to make whatever it is the gene makes. For example there is a gene for Human Growth Hormone. What scientists did was put this gene into the DNA of a bacteria and let the bacteria make lots of human growth hormone.
We can then collect all the human growth hormone and use it as a medicine!