I use the slug bait, the one with the iron. and or the other one, either works.
Caffeine will kill slugs, but the concentration needed is something like 100 tablets of No-Doze per quart of water. Spray on the leaves of the plants. This will dry on the leaves leaving a white powder. Slugs will be killed if they come close. But unfortunately, rain or subsequent watering will wash it away. Actually I did not use No Doze, had some 99% pure caffeine from the lab, tried it out as an experiment. It worked but spraying the caffeine around got me so wired I could not sleep that night. Just by absorbing the mist through my skin. Not really a good cure. Went back to using Slug Bait, it was cheaper and much safer for me to apply.
But the many plants that have caffeine in their leaves, such as Camellia sinensis - tea, a number of Ilex species Yerba matte, and a few other species of plants, that is why the caffeine is there, to deter predation by snails and slugs.