Camping, typically 300mg of Lithium does nothing. It isn't therapeutic until it reaches the range of 900-1500mg and it takes a week or two before it works. Also missing a dose doesn't really matter. From my personal experience, it took a week or two before I'd crash if I quit it. (But I understand the doctor wants to make sure he won't get lithium poisoning and that its safe to increase the dose)

It's also really typical for people that young to deny the diagnosis. I was diagnosed at 19 (almost 4 years ago) and I wasn't med adherent for the first 2 years. I didn't get hospitalized, but I was in and out of my psych every other week. It's typical for people to deny the diagnosis and go 5+ years before they decide to get help. I think the best you can do as a parent is support him if he decides to talk to you again, but not push him into seeing a psych. The brain doesn't stop growing until you're about 25, so a 19 year old does not think with his/her frontal lobes. Rationalizing with teenagers is like talking to a brick wall in most cases. At that age you're driven by emotions, more or less, in your life decisions.

He's probably not going to see the point in medication, especially if he's BP1 and gets manic without psychosis. Hypomania/mania feels good when you're younger and from what I've read it doesn't become as bad until you hit around 30ish+. That could be another reason he is refusing care.

I also agree with cocoa -- there are worse things than pot.