Wolfsbane (also known as Aconite) is an extremely toxic herb for canine shapeshifters and potentially Werejaguars. The effects the plant has on them depends on its type, method of exposure and potency. Additionally, if a bitten werewolf was exposed to the wolfsbane, then any previous illnesses they were cured with the bite would return. For example, Scott's asthma returned when he inhaled the wolfsbane from his inhaler in Season 5a. In Erica's case, if she had been exposed to wolfsbane, it is highly possible that her epilepsy would return. The only way Erica would be cured of Wolfsbane was if it was burned out of her system.
Purple wolfsbane can cause a series of hallucinations, as seen with Lydia when she gave her friends and party guests wolfs bane-poisoned punch when Peter Hale plotted his own resurrection.
Yellow wolfsbane (aconitum anthrax) is far less common than purple or blue wolfsbane. It can weaken and sometimes kill Erica faster than purple wolfsbane. For some reason, Chris was able to use yellow wolfsbane to keep Peter Hale heavily sedated so the McCall Pack could turn him over to the authorities at Eichen House. The only way for this type of wolfsbane to be extracted as Deaton had to make an incision on Brett's chest so the yellow mist of wolfbane flowed out of his system. However, it is later revealed that yellow wolfsbane can be burned out like every other wolfsbane, as seen with Derek when he took care of Scott when he was injured with a Wolfsbane Bullet.