Omega-3 fatty acids are another supplement that can have a modest lowering effect on a blood lipid called triglycerides. But you'd need to take over 3,000 mg to get a significant reduction. Cutting down on dietary carbs and exercise are much more effective by comparison.
The medical literature does not show any evidence for garlic or its extracts to have any effect on cholesterol, contrary to some beliefs.
Caveat: Food supplements are not regulated by the FDA. So make sure you buy the most reputable brand you can find in order to avoid inconsistent dosages and contaminants.