Dealing with the addiction of a loved one can be one of the most difficult experiences a person could have. Often, there is little that you can do other than offer support and let your loved know that you're there if and when he or she needs you.
In a word, addiction is ugly. It has many faces and constantly changes. In 12 step groups, they say that addiction is "cunning and baffling." Addicts say this because its cunning quality is often what leads the addict to relapse. I believe that addiction is equally cunning for the loved ones.
The loved ones watch the addict's personality change and experience first-hand a host of lies and manipulations. Melody Beattie wrote an incredibly important book called "Codependent No More" which describes what can happen to the loved one of an addict. Simply put, they can lose themselves if they try to rescue the addict.
The truth is that there is little you can do when you believe that your loved one has become addicted to something. First, confide in the addict your observations and share your belief that something is going on. Second, let the addict know that you are there to offer support and to help the addict find the clinical support he or she may need. Third and finally, detach a little.
Addiction is a juggernaut and can devestate the spirit and integrity of individuals, relationships, and everything else in its path. Find a good book on addiction today so that you can start coming to grips with what to expect. Whatever you do, understand that there is ultimately nothing you can do to save the person from the pain of their addiction - only the addict has that power.