I've been taking Nal for a few months and I'm wondering how long it is effective on the day you take it. If for instance, you are an all day drinker, and you take the pill in the morning, one hour before drinking, is it still effective if you stop for a few hours and then drink again in the evening? Does a person need to take another pill in the afternoon? I don't drink everyday early, but sometimes I do, and want to make sure the pill is still in effect for the evening. Any thoughts about this?

You'll see several answers to that question, generally they state that you should take a second pill eight hours after the first. Other people take another pill sooner than that. I one time was getting a "crazy" feeling and took a second pill, which then wiped it out. Everybody's different, but the effects of Nal probably start wearing off 2-3 hours after you take it. Everyone's different, though.

http://www.ncbi.nlm.nih.gov/books/NBK64042/

As barryb has already told you, everybody is different. Personally I believe that some people need higher doses of NTX than 50mg daily in general. I think if you take NTX 1 hour before drinking and it reduces or eliminates the euphoria of alcohol, but not e.g. 8-10 hours after that, then you should probably take another pill before drinking again after that time. That's just my opinion though.