Usually withdrawing from social settings. Users just want to be alone and use.

If it starts affecting your life, you can decide to say something, or remove yourself from that person's sphere of interaction.
Intervention isn't always successful. Actually, in my experience, it's never been successful.

This is a very difficult and important subject. I suggest the person who is wondering when to do an intervention, talk to a counselor. I have been in that situation and my worst mistake was being an inabler. We mean well, but in the long run, we really don't help the person with the substance abuse problem, we simply make "shade trees" to keep that person within their comfort level.

The eyes usually give me a good indication of an alcoholic.

When they call in to work sick from hangovers, when they neglect their bills and collection notices pile up, and they drink and blackout not taking care of themselves and live in squalor. After I left my husband over 20 years ago this is what happenned to him that I called his parents to come get him because the bank was repossessing the condo.

You can't help someone who hasnt excepted they have a problem really. stepping in will just move the problem somewhere else

The moment affect your work, your sport/exercise, your relationship with lovers, family, friends any freaking aspect of your life is affected... time to stop, your quality of your life will go downhill... you notice or not makes no difference is downhill... enjoy life until the end, you don't need the abuse.

There is no signs if someone wants to hide it you will never know. To get involved if is not your child is asking for trouble. Most cases is best to let them hit rock bottom, be willing to help them up. Do not use double talk and never blame them.

I am an alcoholic. I can tell you, it's very difficult to tell an addict from an ordinary heavy user. Only the user really knows if they have the power to stop. As to the right time for an intervention, I would say, never! An addict is never going to change until they are ready. Gently let them know how you feel and that you are there for them. That is really all you can do.

Lots of good perspectives and advice here. My 2 cents is everybody has to hit their own bottom before they get scared enough to get help. What is more important is you. If you are emotionally connected to someone with a problem you have to be careful they don't suck you into their black hole of addiction. Lots of 12-step groups, therapists and other support groups can help folks with addicts in their lives. Good luck.