For instance I want to kill a npc via mixing poison to a soup and giving it to the npc, assuming that the npc will drink all the soup, but my poisons damage isn't enough to kill it. If I put more than one dose of poison could I make the soup kill the npc or is one dose same as five doses of poison  ?

For instance I want to kill an NPC via mixing poison in a soup and giving it to the NPC, assuming that the they will drink all the soup. But my poison's damage isn't enough to kill them. If I put more than one dose of poison could I make the soup kill the NPC or is one dose same as five doses of poison?