Are they synthetic or natural ingredients?

It depends on your definition of "synthetic" and "natural". Keep in mind that even most supplements that are labeled as "natural" didn't just appear in nature as they are found in the supplement. The key ingredients in "natural" supplements still had to be EXTRACTED in order to build the formula that makes up the supplement. Thus, you won't be walking down a country road on day and find Pyrodoxal 5-Phosphate (vitamin b-6) hanging off of a tree which you can just pluck off and eat. So you see, "natural" can mean so many different things to different people, it just depends on what YOU call are calling "natural". Keep in mind that in some cases, some vitamins that occur naturally, might not be the best form of that vitamin or may have poor absorption as compared to an "enhanced" form a vitamin or mineral. What I can tell you is this. There is nothing that sticks out in this B-100 formulation that is inherently synthetic. As a matter of fact, Nature's Way went a step further than many of the lower quality formulas and included two different forms each of Vitamin B-2 (Riboflavin -AND- Riboflavin 5-phosphate), Vitamin B-6 (Pyrodoxine HCI - AND - Pyrodoxal 5-phosphate) to make sure that your body has maximum benefit from a more complete form of the vitamin. For example Pyrodoxine HCI form of Vitamin B-6 can have benefits in the body that Pyrodoxal 5-phosphate form of B-6 does not have and vice versa. Additionally, some of the cheaper B-Complex formulas out there will leave out one or more of the B family such as B-12 or some of the B co-factors such as Inositol and Choline. These are all included in this B-100 formula so if you are looking for a well formulated Vitamin B complex that is also affordable then this one is definitely worth giving a try.