how do you get a bipolar person to get help

There is a term I cant remember when a person won't acknowledge or seek treatment for bipolar.  I have a son who is 23 and I have advocated for him and his mental health since he was 7 years old.  When he was diagnosed at 15 he went on Lamictal and Seroquol. This mix worked with minor ups and downs here and there.  He did feel lethargic from the Seroquol and after a couple of years of minor issues, he stopped taking his medicine regularly.  I would dispense his med in a bin for the week, and I would find them in his drawer.  His behavior changed and when I would address the issue, he said that I was intrusive and he blamed his behavior and depression and agitation on situational things.  His coping skills were much improved when on meds, but I could not convince him.  He went away to college in NYC and came back home and he said that he stopped the Lamictal all together and took his Seroquol to sleep.  He didnt even understand that the Seroqual does more than promote sleep.  He had been told and knows that it helps control mania and the agitation he feels.  I am at a point now that I am so frustrated in trying to get him to comply with my suggstions when they have helped him in the past.  I have a daughter who is also bipolar and is so gracious to comply saying that she know without the support of her parents she couldnt do it.  She wants us to help in any way.  She is stable and takes her medicine everyday.  Please give advise.  Being the parent of an adult bipolar person is helpless when the person only deals with issues when there is a crisis.  I keep trying to instill to my son that it is preventative measures that keep someone stable.  He only wants to discuss his mental health when it gets to a point of severe depression of severe anxiety and he is unwilling to deal with his issues to prevent the extremes.  Thanks...A loving mom in la la land...