http://en.wikipedia.org/wiki/Garlic) it states:
The article does not explain how Garlic interacts with the channel blockers though. I do feel sleepy when eating foods that has garlic.
Garlic may interact with warfarin, antiplatelets, saquinavir, antihypertensives, calcium channel blockers, and hypoglycemic drugs, as well as other medications. Members of the alium family might be toxic to cats or dogs. Some degree of liver toxicity has been demonstrated in rats, particularly in extremely large quantities exceeding those that a rat would consume under normal situations.