The effects of garlic preparations, including dehydrated raw garlic powder (RGP), dehydrated boiled garlic powder (BGP) and aged garlic extract (AGE), on the gastric mucosa were determined using a newly established endoscopic air-powder delivery system, which can deliver solid materials directly into the stomach. Among the three preparations, RGP caused severe damage, including erosion. BGP also caused reddening of the mucosa, whereas AGE did not cause any undesirable effects. The safety of enteric-coated garlic products was also determined. Direct administration of pulverized enteric-coated products on the gastric mucosa caused reddening of the mucosa. When an enteric-coated tablet was administered orally, it caused loss of epithelial cells at the top of crypts in the ileum. These results suggest that caution be used with regard to safety and effectiveness when choosing a garlic preparation because some preparations may have undesirable effects, including gastrointestinal problems.