A bard told me that they can't use poisons.
My rogue can - predators can as well.
U buy one from a player who makes em or from a NPC poison vender.
You can't use them til lvl 10. Okay first trick is to find a poison that is good for your level (i.e. not grayed out - and not red and unusable). Okay, this gets confusing because there is ANOTHER color system - the color of the little poison icons themselves - which denotes what they do, not what lvl they are.
Some are more DD, some are slow DoTs, some are DD first then DoT. Most say that 'purple' poisons are the best. But only one rogue/pred per grp can be using that. So buy an orange or whatever as backup.
Caustic assault is a great player made potion - made by scholars, tier 2 artisans. Some of the other pois recipes may still be bugged.
Okay, to use - rt click poison and "equip". It's in the equipables slot. Rt click again and "use". U now get an effect - see the icon? Twelve hourse, or 100 procs - or death. Pretty good. In fact it's too good. Expect nerfage. SoE doesn't like being that nice to us, unless they've reeeeealy abused us first.
Only one poison works at a time. Gray poisons can be "used" but are almost always resisted. Remember, a lot of them work as DoTs. GL