The Night howler serum, also known as the savage serum, is a highly potent chemical drug made from toxic flowers called Night howlers in Zootopia. It was created by the sheep scientist Doug Ramses for the purpose of using it on predator mammals.
Like the natural flowers it is made from, this drug is capable of inflicting highly potent psychological effects on mammals. When exposed to mammals, the serum causes a chemical reaction in the brain that decreases activity in most parts except the cerebellum, which becomes hyper-stimulated, causing the victim to lose higher reasoning functions and lash out at anything that moves. The effect of this Night howler Sickness is that essentially, any mammal reverts to an aggressive, wild, violent state that is described as "Savage".
The effects also appear to be more powerful in this form, as they last much longer, possibly indefinitely.
Role in the Film
Under the orders of his client, Assistant Mayor Bellwether, Doug goes around purchasing Night Howler flowers and sets up a small farm of them in his makeshift laboratory. Once they are fully-grown, he converts them into a serum using a vat and a chemistry set. The serum is then placed within small glass paintball-like pellets and loaded into an air-powered sniper gun, which is used by Doug to dart dozens of predator mammals for Bellwether's plot in order to make prey animals fear the predators.
The farm of Night howlers in Doug's lab that are used to create the serum is destroyed when the lab is accidentally derailed by Judy and Nick and subsequently explodes. After Bellwether's arrest, a cure for the serum is developed for the affected predators, although no details of this cure are given. However, Doug's fate is left ambiguous.