https://wccftech.com/hitman-3-guide-where-to-find-lethal-poison-on-each-level-and-where-to-use-it/

There are many tools of the trade for assassins: sniper rifles, garrotes, chandeliers, bars of soap and let's not forget unicorn horns. But one of the rarer implements of killing, poison, is just as viable as the much more standard tanto or cannonball.

There are three types of poison in Hitman 3: emetic, sedative, and lethal. The first will make the victim sick, often running to the privacy of a bathroom to do so. The second will send the victim to sleep, which can be useful to get around guards, especially if you can get it into the ventilation system. But it is the final one we are most interested in for this guide. Using lethal poison on the target will kill them where they stand, and one of the stops along the way to completing the versatile assassin challenge on each map.