Some manufacturers of vitamin and mineral supplements add synthetics to vitamin products, typically to boost the vitamin's potency.  Many of these synthetics are made from derivatives of coal tar, which is a known carcinogen that is found in cigarette smoke.

5 Steps To Identify The Ingredients On A Vitamin Label

Step 1 - Look for the words "100% natural" on the product's label.
Step 2 - Find the "food source" list on the products label. If the product's label does not contain a list of natural food sources, then the product is most likely synthetic. 
Step 3 - Identify whole foods in the ingredient list instead of the particular nutrient.
Step 4 - Look for salt forms on the product label, a synthetic added to supplements for increasing the stability of the vitamin or mineral. Some of the salt forms to look for include acetate, bitartrate, chloride, gluconate, hydrochloride, nitrate and succinate.
Step 5 - Learn how to read the product's label by looking for keywords that indicate the supplement is synthetic. Words that end in "ide" or "ate" indicate that the product contains salt forms, which are synthetics.

Additionally, the letters "dl" that appear before the name of an ingredient indicates the supplement is synthetic. As an example, look for "fish oils" when buying a vitamin A supplement. If the product's label states "palmitate," it is a synthetic vitamin A supplement.

Common Synthetic Vitamins to Avoid
Vitamin A: Acetate and Palmitate
Vitamin B1 (Thiamine): Thiamine Mononitrate or Hydrochloride
Vitamin B2 (Riboflavin): Riboflavin
Pantothenic Acid: Calcium D-Pantothenate
Vitamin B6 (Pyridoxine): Pyridoxine Hydrochloride
Vitamin B12: Cobalamin
PABA (Para-aminobenzoic Acid): Aminobenzoic Acid
Folic Acid: Pteroylglutamic Acid
Choline: Choline Chloride, Choline Bitartrate
Biotin: d-Biotin
Vitamin C (Ascorbic Acid): Ascorbic Acid
Vitamin D: Irradiated Ergosteral, Calciferol
Vitamin E: dl-alpha tocopherol, dl-alpha tocopherol acetate or succinate
NOTE: The “dl” form of any vitamin is synthetic.

Never take a new vitamin supplement without talking to your doctor or pharmacist first.

For More Information: 

http://www.foodmatters.tv/articles-1/how-to-tell-if-a-vitamin-is-natural-or-synthetic