Many TASER darts don't end up embedding properly in the skin, or come out on their own. Patients with excited delirium (a term that may or may not represent a distinct clinical phenomenon from stimulant-induced psychosis, and which may or may not have been invented by people trying to explain deaths occurring in custody) have been known to be "resistant" to the effects of conducted electrical weapons. It's tough to say whether they were functioning as intended in those circumstances or whether people are just ignoring the stimulus in the face of very powerful competing internal or external stimuli, amped up by really powerful and often dissociative stimulants.

I feel for the people that get called to deal with these people. In the ED I have access to drugs that can bring people down fairly quickly if necessary, and teams of people who are used to physically restraining people without hurting them. It doesn't always work the way we want it to, but we can generally get people safe without hurting them. Cops don't have that training or context, and I have a lot of admiration for the ones that can (and many do) deal with stuff like this without hurting people on a daily basis.

Someday we'll just have ketamine blow darts. (Seriously. Maybe.)