Follow supplement instructions. Don't exceed recommended dosages or take the herb for longer than recommended.
Keep track of what you take. Take only one supplement at a time to determine if it's effective. Make a note of what you take—and how much for how long—and how it affects you.
Be extra cautious about supplements manufactured outside the United States. Herbal products from some European countries are highly regulated and standardized. But toxic ingredients and prescription drugs have been found in supplements manufactured elsewhere, particularly China, India, and Mexico.
Avoid products with a tainted past. A number of herbal weight-loss pills have been found to have serious side effects or to contain prescription drugs or contaminants. For this reason, they're probably best avoided.