I have seen several people claim this has happened in juice...
To be honest its likely not something you could try for or predict, but maybe as an individual you may be lucky enough that it happens for you.
ALSO if someone has low test their hardons may not be that great, then if they cycle their penis will seem alot bigger when really its just functioning at what would be normal for that individual. So many cases, so many mixes of possibilities.
As with your penile size, I say dont think about it too much. I did some research into the "my penis is too small" fear that consumes many people who are hung just fine. Not every chick needs a 10" cock, I dont have one but I also never had a problem doing the job....in fact better than the bigger. Honestly, take care of your body, stay fit and healthy, and learn how to pleasure a woman and you will be surprised.
Unless your suffering from actual medical micropenis or the likes, but there are some new fields of research coming to be involving implants. One of which actually can increase its size, and eventually be removed if you want with no issues. Likely overly expensive and you likely dont need it. Unless your picking up floozies from the bar who have a vagina that looks as wide as a horse shoe.
Have confidence in yourself, you will likely be surprised.