I think I’ll let the character Masaru explain what the drug Shift is as he does during one of his podcasts in book 2:
“Shift is a dangerous drug, usually snorted or shot up intravenously,” Masaru said, “by itself it’s at least as addicting as cocaine or heroin. But it usually comes attached to tiny polymer balls called dendrimers.” Masaru pantomimed two molecules binding with his hands for the video watchers. “Attached to these dendrimers are these sort of guide molecules that give the whole complex quick access past the blood-brain-barrier and into nerve cells. A third set of molecules attached to the dendrimer, a CRISPR/Cas9/gRNA construct, cuts sections of neuroreceptor genes out. That allows DNA transported by the dendrimer to be inserted into the gene,” he touched his index fingers together to mimic DNA strands combining. “This ‘shifts’ the receptors so that they respond more to the drug than they do to your natural brain chemistry. This makes Shift more addictive than any other drug. A person becomes physically incapable of feeling pleasure – and eventually of even cognitive function – without the drug, and taking away the drug becomes fatal. At a certain point, the affect can only be reversed through gene therapy.” He shook his head. “Even then, withdrawal can be long-lasting and more difficult to kick than anything else.”
“Dendrimers are nano-sized, radially symmetric molecules with well-defined, homogeneous, and monodisperse structure consisting of tree-like arms or branches.” (Source)
“Shift was invented somewhere around Detroit,” Masaru continued, “but quickly spread to Chicago. When the Mexican cartels started failing, their drugs shot up in price. And then with the rocky transition to the PRA regional government after the devolution, Shift exploded in popularity all over the place. The Shift gangs, still mostly in Michigan, have been fighting with the PRA government ever since. These gangs are now practically armies. Somehow, weapons seem to be able to get into gang-controlled areas and drugs seem to be able to get out without much trouble. CSA Director Gabriel Mitchell blames Darrel Gibson’s PRA regime, accusing him of collaborating with the Shift gangs. Gibson says this is a lie. Who knows? Both of them lie all the time.”