9. Smoking . We all know smoking is bad for you, but if you've never quit given them up, keep in mind that they will likely reduce your semen volume as well. One study looked at fertile men and grouped them into non, mild, medium and heavy smokers. What is interesting is that hormone levels (testosterone, LH and FSH) as well sperm motility (mobility) and density did not differ significantly among the groups. The one characteristic that did differ was semen volume, which decreased with increasing levels of smoking. 
When your body has enough testosterone, the brain does not send the LH signal to your testicles. Therefore, you will not make any testosterone until your levels drop to below normal and the signal returns, stimulating production. Since you are getting testosterone from an outside source, your brain is most likely not sending that signal to your testicles. Over time, the old adage of “use it or lose it” comes into play and your testicles will shrink in size. The time is different for every man and the amount of “shrinkage” is different for every man. Fortunately, the HCG will quickly restore the size and function.