I just noticed that (I'm at level 20 in normal hardcoe) while fighting some Cazadors (way overpowered) that Boone's life was dropping. I just finished the battle, normally companions health return to full. All of a sudden he started moaning and uttered "looks like I've killed my last legionary" and dropped dead. He was poisoned! This is the 1st time its happened all 65 hours of my game. He was wearing reinforced metal armor (heavy) before, I just put him in mark 2 combat (medium). I reloaded and fought them again and he was terminally poisoned after the battle. I gave him antidote in his inventory and nothing. He wouldn't use it. Nor stimpacks. I ended up blasting him with 20 stimpacks and that cured him. But I AM NOT going to be wasting stimpacks like that. I'm poor enough after a Gun Runner spending spree. I did run further down the hill and fought/killed 2 more Cazadors and he regained health, it would drop to 3/4 and then stop. He was cured after that battle. What the [censored]! That is a GAME BREAKING bug. I've found that people suggest firing him, then going all the way to Novac, and rehire him. That's just stupid. I'm not going to exit hardcoe mode, then reenter either. I want the trophy and that just takes away from the hardcoe experience. Deleting the game data data with the latest patch worries me that the game will run worse. I've had a reasonably crash free experience this time around (2nd playthrough after yellowed PS3). The only other thing I can do is leave him behind and rush them in melee while letting him pick them off with his rifle. But as much as he says he's bad at it, he is really good with melee. Any advice?

Steer clear of Cazadors in the future. Beyond that, I don't know. I've had the same issue, though I didn't need near as many stimpacks to resolve it, usually one or two, three at most. You really should be able to give your followers Antidotes, and have them use them.

For me, Boone seems to be the only companion that stays poisoned after he wakes up on Core mode. He'll die 2 or 3 times before the poison goes away. All others either don't die, or die once and are fine after. And yes, they ought to use Antivenom if I give it to them whilst they're poisoned.

I had this problem with Boone to. Can't remember what I did, but he recovered. Perhaps I gave him antidote or just waited for him to recover. Or did I fast-travel somewhere? Can't remember but you shouldn't have to waste enormous amount of resources on him.

Playing in (PS3) hardcoe mode here and have seen the poison bug occurring several times.
I've noticed however that the poison effect on companions will stop soon after using a dose
of anti-venom on oneself, even if not poisoned after the fight.
After the poison is eliminated (check by entering/exiting the companion wheel a couple
or more times to be sure), the companions can be healed further with stimpacks.

This happened to me with Lily when I was trying to get cazador eggs for the thorn. I ended up using about 30 stimpaks because I didn't know what was going on. Even reloaded and tried over 4 times. Always the same result.

I've read elsewhere that it's a bug arising from the installation of the 1.02 patch. The companions won't use antivenom, and, of course, you can't use it on them, so they're usually a goner if you're playing HC. The worst part is that using a stimpack on them seems to cause them to take the full amount of the poison damage instantly as a lump sum (which, again, usually finishes them off).

There are a few workarounds that have been discovered-- quickly talking to them before they die and sending them back to their home location or the Lucky .38 will avert death, but then you have to go through the annoyance of dropping what you're doing and running off to re-recruit them. I've also heard it told that if you engage another enemy (actively engage-- no snipe-kills. They have to be aware of you) before the companion dies, that'll fix the problem too, but I haven't had a chance to try that one out yet and it sounds like a wives' tale to me.

I have found that if you engage in a battle and finish before they die then the poison is removed. I mailed gamesas support and they replied "that this is not a bug. You can administer antidote and stimpacks through the companion wheel, if not, avoid confrontations between companions and poisonous creatures". WTF! That is not a solution. I tried stimpacks with Boone and I haven't had the dump affect, but I slowly gave him a total of 5 over a course of a minute or two and the poison ran its course and he was fine. Thanks for all the responses. Hopefully it'll be addressed in the upcoming patch.