When neuroscientist George Koob proposed creating a vaccine for addiction 25 years ago, his colleagues thought he was wasting his time. The immune system evolved to prevent infections, not highs from illegal drugs. Prevailing wisdom holds that treating addiction requires months or years of psychotherapy to help addicts change their thought patterns, a difficult process that does not consistently work. But Koob, then at the Scripps Research Institute, wanted addicts to be able to see their doctor for a shot that could keep them from getting high when their motivation to stay clean waned.