Women who fill prescriptions for custom-blended hormone therapy may get capsules or creams that don't contain the correct amount of medicine, a recent study suggests.

Researchers focused on what's known as compounded hormone therapy — prescriptions that are custom-blended by pharmacists instead of factory-made by drug companies and approved for sale by the U.S. Food and Drug Administration (FDA). Sometimes these formulations are marketed as "bioidentical," and touted as being more like naturally occurring hormones than regular pharmaceuticals.

"Unique concerns about safety surround the use of compounded bioidentical hormone therapy, including the lack of regulation and monitoring, the possibility of overdosing or under dosing, the lack of scientific efficacy and safety data, and the lack of a label outlining risks," said Dr. JoAnn Pinkerton, a professor of obstetrics and gynecology at the University of Virginia Health system and executive director emeritus of the North American Menopause Society.

"This study showed that the dose of a compounded product received may be different from the actual prescribed dose," Pinkerton, who wasn't involved in the research, said by email.

For the current study, Frank Z. Stanczyk of the Keck School of Medicine at the University of Southern California in Los Angeles and colleagues tested prescriptions filled at 13 pharmacies for hormone capsules with 0.5mg of estradiol and 100mg of progesterone per gram and for creams with a similar hormone concentration.

In fact, the capsules contained 0.365mg to 0.551mg of estradiol and 90.8mg to 135mg of progesterone per gram. And creams contained 0.433mg to 0.55 mg of estradiol and 93mg to 118mg of progesterone per gram.

Many women have been reluctant to use FDA-approved hormone replacement therapy (HRT) to ease menopause symptoms since 2002, when the federally funded Women's Health Initiative (WHI) study linked treatments containing man-made versions of the female hormones estrogen and progestin to an increased risk of breast cancer, heart attacks and strokes.

Compounded drugs are not FDA-approved, although U.S. regulators may inspect pharmacies to identify problems such as unsterile conditions that could lead to contaminated medicines. Doctors may prescribe compounded drugs to give patients an option that isn't commercially available, such as a dye-free medicine for people allergic to colorings or a liquid or suppository version of a drug that isn't normally sold that way.

Compounded hormone therapy requires a prescription, and may contain the same active ingredients - synthetic estrogen and progestogens - that are in the mass-produced versions. Pharmacists may mix in different inactive ingredients and offer different doses than the FDA-approved drugs.

Women who get the incorrect medication dose in compounded hormones may be at increased risk for certain cancers and other serious health problems, the study authors write in the journal Menopause.

There's also a potential for compounded medicines to contain harmful chemicals or to be contaminated with bacteria, fungi or viruses, they note.

The study was sponsored by TherapeuticsMD, a Florida-based pharmaceutical company that makes menopausal hormone therapies for women.

Beyond its small size, other limitations of the study include the lack of data on whether women would actually be harmed by the varied doses of hormones in the compounded creams and capsules tested.

That's why doctors should prescribe FDA-approved and commercially produced hormone therapy, said Dr. Cynthia Stuenkel of the University of California, San Diego School of Medicine in La Jolla.

"Clinicians need to be confident that the level of the active ingredient is as prescribed," Stuenkel, who wasn't involved in the study, said by email.

"Clinically, the balance between estrogen and progesterone is important, as too much estrogen can overstimulate the uterine lining and contribute to overgrowth and in the long term, uterine cancer," Stuenkel said. "Too little progesterone, which balances the effects of estrogen on the uterus, can have a similar effect."