The use of Allium species (such as garlic, Allium sativum) for the treatment of intestinal parasites, including Giardia, is primarily based on traditional herbal medicine practices. Garlic, in particular, has a long history of use across various cultures as a remedy for a range of infectious diseases, including protozoal infections. Ethnobotanical surveys and traditional medicine texts frequently cite garlic for its antiparasitic properties, and it is often recommended in folk medicine to expel intestinal parasites.

Scientific evidence for the efficacy of Allium species against Giardia is limited but not entirely absent. Some in vitro studies have shown that garlic extracts and their active compounds (such as allicin) can inhibit the growth of Giardia lamblia trophozoites. For example, studies published in journals such as Phytotherapy Research and Parasitology Research indicate antiparasitic activity of garlic extracts in laboratory settings. However, robust clinical trials in humans are lacking, and most evidence comes from animal studies or laboratory experiments rather than well-controlled human studies.

In summary, the use of Allium for Giardia is primarily supported by traditional use with some preliminary scientific support from in vitro and animal studies, but there is a lack of high-quality clinical evidence to confirm its efficacy in humans.