|“||Well, every source says something different. One myth says it causes lycanthropy, which sounds bogus. Another one says that it protects people and another one says, well, it's toxic.||”|
— Jeremy on Wolfsbane in Plan B
Wolfsbane, also known as aconite or monkshood, is an potent herb and a werewolf's most well-known weakness. If a werewolf makes physical contact with wolfsbane in any form, it will burn and weaken them. These affects extend to hybrids as well, who are vulnerable to both wolfsbane and vervain as a result of their dual nature. Its flowers are also used by witches in traditional potion-making in the TVD/TO universe. However, in real life, its leaves and flowers, when handled or consumed in large doses, are very toxic to humans. In the TV series' universe, its effects on humans have never been shown and for all intents and purposes may be nonexistent.
Similar to how vampires are affected by vervain, wolfsbane is shown to adversely affect werewolves. Ingesting wolfsbane severely weakens a werewolf and they appear feverish. Direct skin contact to wolfsbane causes them to be burned so severely that it causes their skin and mucus membranes to smoke slightly at the site of contacy appearing from the contact area. Though a werewolf's enhanced cellular regeneration will eventually heal the wounds, it will take much longer than if it were a regular burn. It has been stated that wolfsbane to werewolves is exactly what vervain is to vampires.
On the night of a full moon, just prior to their transformation into a wolf, many werewolves will dilute wolfsbane in water and drink it to weaken them to decrease the likelihood that they will break out of their restraints and harm or kill innocent bystanders. Both Mason Lockwood and Tyler Lockwood have demonstrated this usage of wolfsbane to subdue oneself prior to their transformations.
Werewolves, despite their healing ability, take much longer to recover from wolfsbane-induced burns and exposure than they would to ordinary burns and toxins, and ingesting diluted wolfsbane has caused many werewolves to become weak, clammy, and feverish for anywhere from several hours to several days, depending on how much they were exposed to at the time. Because of this, wolfsbane is a well-known weapon against werewolves by vampires and humans who are "in the know" about the supernatural to non-fatally subdue them. have long-lasting effects to wolvesbane if ingested. This is because it causes them to become ill. In cases where a werewolf is exposed to large amounts of pure, undiluted wolfsbane, they can be burned so severely that they begin to bleed, as shown when Damon Salvatore chained Mason Lockwood up and force-fed him an entire bud of wolfsbane, which caused him to cough up blood and stomach acid. According to Jules, an experienced werewolf can use their heightened awareness to "sniff out" wolfsbane, such as when she sensed that Damon had laced her drink with it.
A werewolf's weakness to wolfsbane has not yet been explained in the show, although looking at the similarities at their specific weaknesses, this could be attributed to the creation of the first werewolves, much like how vervain was indirectly involved in the creation of the first vampires and became a weakness for their species as a result.
It was implied that a small mixture of of crushed aconite flower and jimson weed combined in a mug of tea can be drunk by a pregnant werewolf to induce a miscarriage, a method that Hayley Marshall briefly considered when she first learned she was pregnant with her daughter Hope.
It has been common knowledge among all that have dealt with werewolves that they are vulnerable to wolfsbane. As hybrids are a relatively new species with abilities of werewolves, it is expected that they would possessed at least some of the common weaknesses of werewolves.
So far, weaponised wolfsbane has only been shown to be used on hybrids. Katherine Pierce used wolfsbane grenades to slow down Klaus' sired hybrid army. Damon also used a wolfsbane grenade on the unsuccessful and rabid hybrid Ray Sutton, who had been forced to play a game called " truth or wolfsbane" with Stefan Salvatore prior to his transformation.
- Until now, every single wolfsbane administration has been done directly on the werewolf. That is, wolfsbane has either been voluntarily consumed by werewolves/hybrids or involuntarily forced upon them.
- Unlike vervain, wolfsbane is not consumed by humans to protect them from werewolf attacks, likely because 1) the werewolf genocide that has gone on for centuries has reduced their numbers significantly, and 2) most triggered werewolves take countermeasures to ensure that they do not expose their supernatural identities or harm civilians on the full moons, either by locking themselves up in secure locations or by going into the remote wilderness where they can run free without risk of running into civilization, both of which have likely reduced the number of humans who are aware of the werewolves' existence. This seems to be supported by the fact that even the majority of vampires believe werewolves to be merely a myth.
- It is also possible that, like in the real world, wolfsbane is extremely toxic to humans, which would prevent them from ingesting it as preventative measure against werewolf attacks.
- Wolfsbane seems to have no affect over untriggered werewolves.
- Experienced werewolves can smell wolfsbane if it's laced in their food or drink.
- Though wolfsbane and vervain are often compared due to the similar reactions exposure causes to werewolves and vampires, respectively, it can be argued that wolfsbane exposure for a werewolf is much more severe than vervain exposure to a vampire. The side effects vampires experience from ingesting vervain can be counteracted by the vampire in question feeding on blood to help speed up their recovery, whereas werewolves simply have to wait for their accelerated healing to finish purging it from their system on its own, a process which takes considerably longer than it would for a vampire.