There are no proven side effects that come with consuming a Tequila worm. While the worm is popularly called the tequila worm, it is only found on the bottom of a bottle of mezcal, a variety of tequila obtained from distilling blue agave and similar plants. The meriposa worm is grown on agave from which mezcal is made, and when a worm is added to the mezcal, it is known as mezcal con gusano.
Consuming the worm after drinking mezcal is a popular tradition among many communities, but it is not clear where the tradition originated. Some believe that the adding the worm in a bottle of mezcal signifies the purity of the alcohol, as it hinders the disintegration of the worm. Others believe that it is merely a marketing strategy among Mexican liquor producers.
While it's documented in media that the eating the worm causes hallucinations, this has yet to be medically proven. The worm is pickled in alcohol for more than a year and is made sure to be free to pesticides, before being added to mezcal. It is also a popular delicacy in Mexican restaurants, and is said to have positive psychological effects.