The Ache: Whether from morning sickness, chemotherapy or a bad trip in a car or a boat, nausea is a common complaint.

The Claim: Lollipops in flavors such as green apple or ginger, or infused with a vitamin, can settle the stomach and keep the queasy feeling at bay.

The Verdict: While the lollipops haven't been tested in a clinical trial, some of their ingredients, including ginger and vitamin B, have been shown in studies to combat nausea.

Queasy Drops Joshua Scott for The Wall Street Journal

Preggie Pop Drops Joshua Scott for The Wall Street Journal

The idea of a treating nausea with natural ingredients is appealing, as many prescription anti-nausea medications have side effects, such as making you drowsy, says gastroenterologist Patricia L. Raymond, an assistant professor of clinical internal medicine at Eastern Virginia Medical School in Norfolk, Va. However, she adds, there is insufficient proof that any of the candies are effective.

A common ingredient in nausea-fighting lollipops, lozenges and chews is ginger oil. Preggie Pops, aimed at combating morning sickness, and Queasy Pops, popular among chemotherapy patients, are sold at a suggested retail price of $4.50 for seven lollipops; each ginger-flavored pop contains 62 milligrams of ginger, says Julie Davine, operations manager of Three Lollies LLC of West Hills, Calif., which sells the candies.

Studies have shown ginger is helpful for combating nausea that results from a wide range of causes, including chemotherapy. In two recent studies, ginger successfully reduced nausea caused by retroviral drugs and by surgery.

Scientific literature shows "increasing support" for ginger as a treatment for morning sickness, says Anne Matthews, associate professor of nursing at Dublin City University in Ireland and co-author of a recently updated Cochrane Collaboration review of 37 trials on natural therapies for pregnancy-related nausea.

Still, the growing body of positive results for ginger as a nausea treatment can't be used to demonstrate efficacy for the lollipops, says Lawrence Leung, co-author of a review of ginger research published earlier this year in the Journal of the American Board of Family Medicine. The candy likely contains far smaller amounts of ginger than the amounts studied, Dr. Leung says. The six studies in Dr. Leung's review, which found ginger effective in morning sickness, used 750 to 2,500 milligrams of ginger daily, taken as capsules or as a powder in food.

Ms. Davine of Three Lollies says details on how its ginger oil is made are "proprietary" and the company doesn't know how its ginger-oil formulation compares with capsules. She says the act of sucking itself may help alleviate nausea and some of the flavors in Preggie Pops—such as sour lemon, sour tangerine and peppermint—appear to be soothing to the stomach.

Aromatherapy with lemon oil was effective against morning sickness in an Iranian study published earlier this year. Mint aroma was found ineffective in a 2012 study. Those results, however, don't necessarily apply to candy with those oils, scientists say.

Another popular ingredient in some anti-nausea candies for pregnant women is vitamin B6. It was shown to be effective against morning sickness in patients taking 10 milligrams every eight hours, and in another study when a dose of 25 milligrams was used.

Three Lollies' Preggie Naturals chews, $5.95 for 15, each contain 10 milligrams of B6. B-natal cherry lollipops and green-apple lozenges, from Everidis Health Sciences of St. Louis, each contain 25 milligrams and they cost $15.99 for 28.