First of all I want to thank everyone for their responses -- I definitely didn't expect to get so many replies so quickly!
As to whether I can stop when I start, I guess the answer would be it depends. In situations where it really wouldn't be appropriate for me to get drunk, i.e. family get togethers, work-related parties, etc, I don't have all that much trouble just having a few and stopping. A lot of times if I know I have to drive home I will only have a few so I don't risk a DUI. However, I do go out drinking literally every weekened night, a lot of times including Thursdays and on a lot of these occasions I will get more drunk than I planned.
I should mention that I'm in college so a lot of these drinking behaviors are more or less "normal" for a lot of my peers. I'm not really worried so much about the drinking itself, but more the drugs (especially opiates). I definitely use more drugs more often than most of my peers. A lot of times I will plan to quit this or that but then later on I will think "oh well maybe just this one last time". I've definitely tried to quit marijuana more than a few times and failed. Recently I've said that I'm quitting opiates several times and have yet to make it more than a week without them.
As far as having a problem with complete abstinence I guess I can do it for a few days and I don't freak out or anything its just that it gets boring after a while I guess. For me and most of my friends getting ****** up is just the default activity we do together so without it I'm kind of left with nothing. I guess this is what I'm worried the most about -- that I'm not really getting anything out of life other than getting ****** up.
I should also mention that I suffer from anxiety/depression and my self-medication with drugs/alcohol I feel may be preventing me from making any real progress on this.
The problem I guess that I have is that I'm worried about this being a slippery slope. Right now I feel like I'm just a few squares south of having a "normal" life but I'm also just a few squares north of being a junkie. Recently with opiates I've had trouble controlling my use when I want to and also when I use I often I guess you could say "fantasize" about using everyday and try to figure out ways for it to be financially feasible. I want to prevent myself from falling deeper into addiction but I guess I'm not completely sure I'm willing to completely change my life, isolate myself from using friends, etc and follow the NA/AA 100% sober lifestyle.
I plan to go to an NA meeting on Friday so hopefully that will give me a little more insight on what its like!