There are a few kinds of “detox kits” on the market. These are kits that purport to help people flush a particular drug out of their system. They usually take the form of drinks or pills.
While generally legal, the quality of these products is quite poorly regulated.
Most common by far, and one of the only groups of products that seem to have at least moderately positive user feedback, are products designed to cheat THC drug tests. Some take several days to work, while other more expensive products claim to work faster.
When these products are advertised as “detox kits,” they don’t mean “detox” in the true sense. They won’t help you rapidly go through withdrawal to clear your body of its physical dependence on a drug as some medical procedures try to. More or less, the goal of these kits is to cheat drug tests.