Poisoned candy myths are mostly urban legends about malevolent strangers intentionally hiding poisons, drugs, inedible items or sharp objects such as razor blades in candy, which they then distribute with the intent of harming random children, especially during Halloween trick-or-treating. These myths, originating in the United States, serve as modern cautionary tales to children and parents and repeat two themes that are common in urban legends: danger to children and contamination of food.

There have been confirmed cases of poisoned candy, but these are rare. No cases of strangers killing children this way have been proven. Commonly, the story appears in the media when a young child dies suddenly after Halloween. Medical investigations into the actual cause of death have always shown that these children did not die from eating candy given to them by strangers. However, in rare cases, adult family members have spread this story to cover up filicide or accidental deaths. In other incidents, a child who has been told about poisoned candy places a dangerous object or substance in a pile of candy and pretends that it was the work of a stranger. This behavior is called the copycat effect. Folklorists, scholars, and law enforcement experts say that the story that strangers put poison into candy and give that candy to trick-or-treating children has been "thoroughly debunked".

Worries that candy from strangers might be poisoned have led to the rise of alternative events to trick-or-treating, such as events held at Christian churches, police and fire stations, community centers, and retail stores. The primary risk to children's health and safety on Halloween is being killed by a car.

Claims that candy was poisoned or adulterated gained general credence during the Industrial Revolution, when food production moved out of the home or local area, where it was made in familiar ways by known and trusted people, to strangers using unknown ingredients and unfamiliar machines and processes. Some doctors publicly claimed that they were treating children poisoned by candy every day. If a child became ill and had eaten candy, the candy was widely assumed to be the cause. However, no cases of illness or death were ever substantiated.

In the 1890s and 1900s, the US Bureau of Chemistry, in conjunction with state agencies, tested hundreds of kinds of candy and found no evidence of poisons or adulteration. These tests revealed that inexpensive glucose (from corn syrup) was in common use for cheap candies, that some candies contained trace amounts of copper from uncoated copper cooking pans, and that coal tar dyes were being used for coloring, but there was no evidence of the many types of poison, industrial waste, garbage, or other adulterants alleged to be present. Eventually, the claims that children were being sickened by candy were put down to indigestion due to overeating, or to other causes, including food poisoning due to improper cooking, hygiene, or storage of meat and other foods.

The prevalence and persistence of these myths during the 1960s and 1970s, a time of social upheaval, greater racial integration, and improved status for women, reflected societal questions about who was trustworthy. Because society was struggling with questions about whether to trust neighbors in newly integrated neighborhoods, or young women who were publicly rejecting the subservient, motherhood-focused roles previously assigned to women, these stories about unidentifiable neighbors allegedly harming random, innocent children during an event intended to bring happiness to these children caught and retained the public imagination in a way that accurate stories about a judgmental neighbor, an abusive parent, or an adult carelessly leaving harmful chemicals where children can reach them, would not have. An academic view sees this as an example of a rumor panic, with Halloween developing as a carnival-like folk institution – meant to release social tensions – losing its functionality as neighborhoods themselves break down (for various reasons).

Due to their fears, parents and communities restricted trick-or-treating and developed alternative "safe" events, such as trunk-or-treat events held at Christian churches. This collective fear also served as the impetus for the "safe" trick-or-treating offered by many local malls.

This story also promoted the sale of individually wrapped, brand-name candies and discouraged people from giving homemade treats to children.