The temptation here is to look at this thing section by section, chapter by chapter to describe and evaluate the book. I tried that, and it was going to be impossibly long. But that's not the kind of blog I do, and I'm not qualified to analyze this based on the scientific merits (although I have some pretty strong, and fairly informed, opinions).
In documentaries, there are (essentially) two approaches: in the first, the filmmaker is absent -- not in the shot, not doing the narration (or if there's narration, it's just describing what's on screen, etc. -- no editorializing, no "I"); in the second, the filmmaker is part of the story, possibly a large part of the story, but their presence, their voice is all over the place. There are great movies in both approaches, and forgettable (or the kind you wish were) in both. It mostly depends on the subject, the filmmaker and the viewer's tastes. Most non-fiction books take the former approach, but every now and then (but I think more "now" lately than "then") you get the latter. Chasing the Scream was a big case of the latter. On the whole, I think that was an error -- there was just too much Johann Hari throughout -- often at odd times, too. Now, eventually, he does describe his connection to this subject, and it makes sense. But it doesn't mean he did it right throughout, and by the time he described why he did it, I didn't care, I was just annoyed that he had.
Hari builds the opening sections of his book on a triad: law enforcement, addict, drug dealers. Using profiles of individuals -- with knowledge gained either through interviews or documents -- and then extrapolating a little from them (not as much as he could've) tries to examine where each of these groups has been, is now, and will be as our "War on Drugs" continues to be fought as it is. While Hari clearly has subjects he prefers over others in these sections, he tries to treat most of the people he profiles with compassion, with the understanding that they're people trying to do the best thing. Now, sure, he doesn't say that about the Mexican cartel guys killing for competitive advantage, don't get me wrong.
From there, Hari goes on to look at the nature of addiction, to critique what so many are taught today is the cause of addiction, and what's the best form of treatment. You can see the nugget of that in this video: Everything We Think We Know About Addiction Is Wrong
. Especially given his take on the Addiction, his approach to legalizing distribution and types of treatment he pushes makes sense.
From there, Hari looks at some treatment types and programs that have had the kind of success he hopes for, some municipalities and nations that have taken various steps towards legalization/decriminalization of drugs -- including interviewing former heads-of-state. He looks at the recent campaigns in Washington and Colorado to legalize marijuana use -- how they were radically different, and what wouldn't work in Washington (or most anywhere else), hit the sweet spot for Colorado. Naturally, from there, it's a call to arms to get something done to improve the terms of the Drug War (mostly through stopping fighting it). But he does so in very vague -- do what you think is best, because he doesn't have all the answers -- terms
If you can get past Hari's constant use of bringing himself into every bit of this book, and can listen to what he's saying, this is a very well put together book and well-worth your time and attention. And even if you can't get past Hari, you should try -- these ideas, this subject -- is important enough. He may not change your mind, but he will make you think about your positions.