Deca has been shown in several studies to cause total shutdown of natural testosterone with just 100mgs! That is a tiny amount. It goes to show that if cycle doses are use, there is going to be some issues, 100%.
*edit* And never listen to an 18-20 year old at the gym, or anywhere else in life when it comes to important, life altering decisions. I dont even listen to them when they ask me a question at the gym. just kidding, but hopefully you get what I am saying. Their "sky high" natty test is at rock bottom about a week after that first injection.