Cannabis

It was called the M1 Resuscitation Tube. It had one end that plugged into the outlet valve well of the M17 protective mask, and the other end went into the victim's mouth. The Army's official reason for getting rid of this was that the rescuer could be overcome by the poison gas.

The real reason they got rid of it was the end for the outlet valve well looked, and functioned, exactly like the bowl of a pot pipe. The government finally came to the realization that if you were going to smoke that shit even when you weren't supposed to, the least you could do is buy your own paraphernalia.