Fear (Abbott novel)

"Fear" is a 2006 thriller by Jeff Abbott. Texas Monthly described the novel as a "pharmaco-thriller about a clandestine medical clinic".
Plot.
Miles Kendrick suffers from Post-traumatic stress disorder and is in a witness protection program. When his psychiatrist is targeted and killed he feels somehow responsible and sets about trying to find out why she was killed and avenge her death. A constant companion is his best friend whom he killed some time in the past.