Sinclair came to believe that people develop drinking problems through a chemical process: each time they drink, the endorphins released in the brain strengthen certain synapses. The stronger these synapses grow, the more likely the person is to think about, and eventually crave, alcohol—until almost anything can trigger a thirst for booze, and drinking becomes compulsive.Sinclair theorized that if you could stop the endorphins from reaching their target, the brain’s opiate receptors, you could gradually weaken the synapses, and the cravings would subside. To test this hypothesis, he administered opioid antagonists—drugs that block opiate receptors—to the specially bred alcohol-loving rats. He found that if the rats took the medication each time they were given alcohol, they gradually drank less and less. He published his findings in peer-reviewed journals beginning in the 1980s.
Subsequent studies found that an opioid antagonist called naltrexone was safe and effective for humans, and Sinclair began working with clinicians in Finland. He suggested prescribing naltrexone for patients to take an hour before drinking. As their cravings subsided, they could then learn to control their consumption. Numerous clinical trials have confirmed that the method is effective, and in 2001 Sinclair published a paper in the journal Alcohol and Alcoholism reporting a 78 percent success rate in helping patients reduce their drinking to about 10 drinks a week. Some stopped drinking entirely.