Some supplement makers have been known to scrimp on ingredients or allow pesticides or carcinogens to get into their products. Be wary of products marketed via e-mail alerts or over the Internet. If you aren't sure about a company, ask a pharmacist or nutritionist. Look for an expiration date.
Some supplements lose their potency after time.
Read the label and stick to the dosage. Exceeding the recommended dosage can be dangerous. Watch out for combining things with similar effects, such as two stimulants or two depressants. Consult with your doctor before mixing prescription drugs and herbal supplements. Some supplements can counteract drugs' effects.