You couldn't find a better example that illustrates the problems associated with favoring synthetic supplements over whole foods than this European study that shows how garlic supplements have no effect on a number of risk factors for heart disease.
A randomized study of 90 overweight smokers measured the effect of garlic powder, a placebo and the always problematic Lipitor on cardiovascular disease and, in particular, inflammation and blood vessel function.
No surprise, patients who took the garlic supplement for three months showed no improvement in their cholesterol levels or any other signs of heart disease while those taking Lipitor experienced drops in C-reactive protein and TNF-alpha (both signs of inflammation) and their cholesterol levels.
The catch about the aforementioned study: Patients benefit the most from garlic and onions when eating them fresh. Also, the active ingredient in garlic -- allicin -- dissipates an hour after cutting it, meaning a garlic pill won't do your health any good.
Your best options: Compressing garlic with a spoon before swallowing it or adding it to your daily vegetable juicing regimen.
American Journal of Clinical Nutrition, Vol. 84, No. 6, December 2006: 1324-1329Reuters January 7, 2007