Can didrex show up as amphetamine in a drug screen?

Yes. Benzphetamine is a "precursor" to both methamphetamine and amphetamine, i.e. As the body breaks it down, it becomes amphetamine and methamphetamine before being eliminated. One study* showed that administration of Benzphetamine resulted in measurable amounts of amphetamine and methamphetamine in the urine. *cody jt, valtier s. J anal toxicol. 1998 jul-aug;22(4):299-309.