I too was in the Marine Corps and had a lot of guys that stood by my side that were on AS...
I believe that you should not do the cycle before you leave b/c when you get to bootcamp you will be broken down into the person that they want you to be...there will be no weight lifting invovled. You will be physically and mentally tested every day and I would think that a person going through that kind of training would want to be going through it with a clear head. I think like a couple other people on here also...you should wait until bootcamp and when you get settled into your final duty station then take a look at your surroundings and get comfortable in them. Find out what you can and can't get away with and then see how a cycle would fit into your schedule.
I have only seen one person get kicked out for AS use and that is b/c on our trip to Somalia he gained 35 pounds and this son of a bitch got huge!
I will go far to say that when I was in I watched our corpsman give shots to my Capt. and other members of my team. I was not in a big group, but a lot of people did them.
Just be careful and watch your ass!

BTW// 0311 Division Recon Camp Pendelton 92-96

Good Luck!