if you're talking about a 24 month period, there really isn't a specific steroid that you can take for 24 months that won't have some sort of side effect. Be it, hair loss, acne, liver damage, ulcers, etc... There's a wide range of side effect, mostly caused from abuse, but everyone's body is different, and reacts differently to all chemicals put into it.
The number one form of steroid abuse, is not allowing the body proper time to recoop after a cycle. A lot of guys cycle one group of steroids for 8 weeks, then an alternate set for the next 8 weeks, and then back and forth. Probably a best bet is to keep a cycle under 8 weeks, and allow your body 8-12 weeks of recoop time, using different supplements to help the process, then cycling again.
Your best bet is to visit a steroid forum on the net, yes there are some great ones out there.
<-- been researching alot, did a cycle years and years ago, but I dont' feel I got what I could out of it