One who is in good health and takes vitamins as supplements or for prevention purposes should preferably take vitamins only with a reliable hechsher. Currently the Star-K certifies various Shaklee vitamins. Where such products are unavailable, one should ask his Rav or Kashrus agency about vitamin components of non-certified brands to determine whether the product can be taken. Every year Rabbi Gershon Bess Shlita researches thousands of medications for a Pesach guide published by the Kollel of Los Angeles. It is important to note that this and other such lists consider the chometz issues, not the Kashrus considerations presented above.
Flavors also require research.
In addition, liquid medications containing grain alcohol derived from wheat should be considered chometz. In most instances, something containing chometz may not be used even externally and should be sold with the chometz. Corn syrup is also commonly used in liquid medications. Because a choleh sh'ain bo sakanah. In addition, kitniot based shampoos and cosmetics are also included in this list because they are not taken internally.