I believe it's talking about living the real life of a heroin addict, comparing that to the celluloid life of a cowboy in a Western. It isn't, IMO, a comment on whether that life is good or bad or whether the person is living life to the full, but simply that there is a certain excitement of being a law-breaker, and a constant chase (or struggle) to feed the habit.

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Note added at 28 mins (2012-07-07 17:22:01 GMT)
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"Living the life" is the normal expression. Perhaps the author avoided that to convey that a heroin addict could be said to exist rather than actively living the life, as the latter suggests an element of control over your own life.

I agree with Sheila's gloss of 'living the life', but I interpret it completely differently, more in line with Salman's explanation. The thrill is living the life of an outlaw/anarchist/anti-hero by thieving, dealing and shooting up.

Another highly relevant gloss to my mind is 'day in the life' - both the Solzhenitsyn story and the Beatles song.

being in the life => living a life of contravention or in conflict with mainline society values

in the past " being in the life" referred to living as a prostitute. then it was expanded to embrace gays and lesbians and also drug addicts - so it refers to living a life of contravention or at least one that conflicts or goes against the mainline society values


The findings reveal that prostitution was primarily a means to an end for these women and that, despite many negative aspects of their experiences, the positive aspects of 'being in the life' served to keep women involved in prostitution.
http://www.repository.upenn.edu/dissertations/AAI3447144/

contravention
con·tra·ven·tion/ˌkäntrəˈvenCHən/
Noun:
An action that violates a law, treaty, or other ruling.

The Butch Caucus
www.thebutchcaucus.blogspot.com/
Black gays and lesbians, described in Harlem vernacular as being “in the life,” provided entertainment in the form of private parties, sometimes fund raisers, and

The Gay Harlem Renaissance | Welcometoharlem's Blog
www.welcometoharlem.wordpress.com/2011/.../the-gay-harlem-r...
28 Jul 2011 – The Harlem of the 1920s, which produced a flowering of art, music and writing, was indisputably gay. Being “in the life” was part of the..

Coming out or staying in? - Atlantic City Lesbian Relationship ...
www.examiner.com/article/coming-out-or-staying-in
24 Jan 2011 – Being in the life does not have to be visually seen to the “naked eye”. ... you wear or how you appear to the public does not make you a lesbian.

AIDS AND CRIMINAL JUSTICE - Annual Review of Anthropology ...
www.annualreviews.org/doi/abs/10.1146/annurev.anthro.30.1.4...
The National Institute of Drug Abuse (NIDA) has been part of the National Institutes ... all public health facets of drug addiction and drug “abuse”—biomedical as well social, .... “Being in the life” has its romantic side for those who are involved.

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Note added at 21 hrs (2012-07-08 14:50:09 GMT)
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Opinion: neutral
Comment: It's not as generic a term as you make it out to
be; it carries the meaning that you claim is "in the past:"
to refer to a particular lifestyle. Hence, the expression
"being in the life," where "the life" can be
prostitution, addiction, etc.

seriously - I do not get your point!!

When the expression "in the life" is used, it is always with regard to a particular lifestyle, never as a generic expression to denote any unorthodox lifestyle. Hence "in the life," where the "the" refers to a particular way of living.

Today, "in the life" commonly refers to living life as a gay, bisexual, lesbian or transgendered (LGBT) person, as most of the links in airmailrpl's explanation tend to support, but it can also refer to prostitution, drug addiction, or other activity which is derived from a separate subculture.

That "in the life" is specific rather than general is exemplified in In The Life Media, a company that for the past 20 years has produced an LGBT documentary series, aptly called "In the Life," for the PBS network:
http://www.itlmedia.org/


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Note added at 22 hrs (2012-07-08 15:51:18 GMT)
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The target term should read "desirable" rather than "desireable."