Poisons in the Wizarding world are substances that cause harm, illness, or death when ingested, inhaled, or introduced into the body through contact or injury. They are not a single type of substance but a broad category that includes brewed Potions, venoms from magical creatures, and toxic parts of magical plants. Their appearance is highly variable. A poison can be a simple liquid indistinguishable from a harmless beverage, such as the oak-matured mead poisoned by Draco Malfoy, or a thick, potent fluid like the deadly green venom of a Basilisk. Some magical objects, like the cursed opal necklace from Borgin and Burkes, are imbued with poisonous curses that activate upon touch. Others may be gaseous, like the fumes from poisonous candles.
The primary function of any poison is to inflict harm. The effects can range from mild irritation, such as the boils caused by undiluted Bubotuber pus, to swift and certain death. Poisons are a common tool in the Dark Arts, often favored for assassinations due to their stealthy nature. Beyond simply killing, some poisons possess unique magical properties. The most significant example is Basilisk venom, which is one of the few known substances powerful enough to destroy a Horcrux. This property stems from its immense destructive power, which leaves an object damaged beyond magical repair. Poisons and their components are also crucial ingredients in the art of Potions. Valuable substances like Acromantula venom and Doxy venom are sought after by potioneers. The study of poisons is intrinsically linked to the study of their cures; knowledge of antidotes, such as the Bezoar, is a vital part of a Potions education at Hogwarts.
Throughout the Second Wizarding War, several poisons and venoms played a significant role:
Poisons serve as a key plot device and a thematic element, representing an insidious and cowardly method of attack. Albus Dumbledore himself notes that Lord Voldemort prefers others to do his killing and that poison is a weapon often used by those who fear a direct confrontation. This theme is central to Draco Malfoy's arc in Harry Potter and the Half-Blood Prince. His repeated, failed attempts to assassinate Dumbledore using poison highlight his desperation and his moral conflict, as he is unable to commit murder directly. Furthermore, the existence of poisons necessitates knowledge of antidotes, underscoring the life-saving importance of Potions proficiency, as demonstrated by Harry's use of the Bezoar to save Ron. Finally, the destructive power of Basilisk venom is absolutely critical to the main plot of the series, as it provides the means to destroy Voldemort's Horcruxes and ultimately defeat him.