You can find it in gummy candies, bottled water, cosmetics and even beer. Iowa State University Extension agronomists report that they get calls every day from Iowa farmers asking if they can grow it.

Hemp, a cannabis plant in the same family as marijuana, has become a trendy new potential crop — and ingredient — after the 2018 farm bill loosened regulations to allow U.S. farmers to grow it.

With more states approving the distribution of marijuana for med­icinal or recreational use, cannabidiol (CBD) — a chemical derived from hemp — is now appearing in a variety of food, beverage and cosmetic products.

Dubious marketers claim that CBD can cure a wide variety of health ailments, from insomnia and pain to hair loss to cancer.

Yet health experts stress that CBD isn’t a cure-all and shouldn’t replace proven medical treatments.

We asked Dr. Michael Ciliberto, a pediatrician at the University...