I'm a 18 year old but i'm little short for my age thinking to use growth hormone. what are the possible side effects of growth hormone for growth?

Not going to help: At your age, growth hormone is going to be a waste of money. It is extremely unlikely that you are going to get any height out of growth hormone at this stage of your life. It may increase muscle mass and bone density, but you are not going to get extra inches. Risks of use of growth hormone abound. You need to accept your current stature, and discard the idea of growth hormone being the solution.

Growth hormone: Before you get involved with growth hormone see your doctor to see if you still have any growing to do. He can order an xray of your left wrist to determine your bone age.

Worthless expense: The true prescription HGH would run you 10-15K out of pocket/yr while the OTC "boosters" don't really boost anything but their own profits.At 18 your growth centers in your long bones are likely closed, so your linear growth is done.If they are open you would only get to your final height sooner, not add anything.