Why should we be aware of manufacturers and the supplements they are trying to sell?

Because they're classified as food products, not medicines, so they aren't regulated by the strict standards governing the sale of prescription and over-the-counter drugs.

Under the Dietary Supplement Health and Education Act of 1994, the dietary supplement manufacturer is responsible for ensuring that a dietary supplement is safe before it is marketed. FDA is responsible for taking action against any unsafe dietary supplement product after it reaches the market.

Explanation:

A firm is responsible for determining that the dietary supplements it manufactures or distributes are safe and that any representations of claims made about them are substantiated by adequate evidence to show that they are not false or misleading.

>> so dietary supplements do not need approval from FDA before they are marketed

The FDA has comprehensive regulations for Current Good Manufacturing Practices for those who manufacture, package or hold dietary supplement products that manufacturers must follow. These regulations focus on practices that ensure the identity, purity, quality, strength, and composition of the products