Allicin, a sulfur-containing compound derived from garlic (Allium sativum), has been investigated for its antimicrobial and antiparasitic properties, including its effect on Giardia lamblia, the causative agent of giardiasis. In vitro studies have demonstrated that allicin exhibits inhibitory effects against Giardia trophozoites. For example, a study published in Parasitology Research (2009) found that allicin significantly reduced the viability of G. lamblia in culture. The proposed mechanisms involve allicin’s ability to react with thiol groups in parasite enzymes, thereby disrupting metabolic processes essential for Giardia survival.

However, while laboratory data are promising, clinical evidence in humans is limited. Most research supporting allicin’s use against Giardia comes from animal models and cell cultures, with only a few small-scale human studies or case reports. There are also some traditional uses of garlic for intestinal parasites, but the specific role of allicin and its efficacy for treating giardiasis in humans remain insufficiently validated by large, controlled trials. Thus, while scientific studies provide a basis for potential anti-Giardia activity, the overall evidence is preliminary, warranting a moderate-low rating.

In summary, the use of allicin for Giardia is supported by early-stage scientific research, particularly in vitro, but lacks robust clinical validation. Further human studies are required to confirm efficacy and safety for this indication.