Reading through this thread I wonder if Tanya had been an MD vs a veterinarian, would she have made up the suicide syringes or not. As a vet, she will have had euthanization as a regular part of her practice and training/philosophy about when to use it. Most MD's don't/wouldn't, I think.

And since Saul worked with her at times, I'm sure he had the same understanding/philosophy about it. In other words, if there had been a different doctor at the colony or someone other than Saul digging in there, we wouldn't have had the syringe that kept Mucho Macho Victor from becoming the baddest ass Zed around.... (great f'n scene!)

Since Little One Arm got stitched by the minigun right after that, we have no idea how the drugs affect the Zeds. Just that a needle to the eye distracts them pretty well.