Long story short, your brain is addicted to the endorphin rush that results after consuming alcohol. You can abstain for a period of time but due to the alcohol deprivation effect your urges to drink alcohol only increase as you abstain for longer periods of time (hence the AA mantra "Once an alcoholic, always an alcoholic.") The Sinclair Method gets around this by attacking your brains relationship with the alcohol endorphin rush. Long story short, you take an opioid antagonist (endorphin blocker) before you drink, typically Naltrexone or Nalmefene, which slowly trains your brain to no longer associate alcohol with pleasure. Check out the book for more information.
I was a heavy drinker and alcohol was destroying my life and after 4 months of TSM, I was drinking at a safe level and now one year later I am completely sober. I could continue to drink if I wanted to, with Naltrexone, but at this point I am ready to start a new life without alcohol and leave that all in the past. I believe 40% of TSM users choose to abstain completely and the other 60% choose to drink socially in moderation. It is up to you, which highlights the power of this system. Having complete control over my drinking after being out of control for years is nothing short of a miracle.
(You may also run into systems where you take Naltrexone on days that you don't consume alcohol. This is something different, and it may work for you, but my experience is with TSM which requires you only take Naltrexone before drinking)
[1] https://www.dropbox.com/s/60fs7gmvbyzs1kk/Cure%20for%20Alcoh... [2] https://www.reddit.com/r/Alcoholism_Medication/