HRT carries some risks
Using patches instead of pills could cut the risk of one of the lesser-known complications of hormone replacement therapy, a study of 1m women says.
Some women on HRT develop gallbladder problems which require surgery to remove the organ.
An Oxford University team reported the rate of operations for patch-wearers was substantially lower than for those having HRT in pill form.
One could be avoided for every 140 people changing to patches, they said.
The gallbladder is a small organ, attached to the base of the liver, which stores and concentrates bile, a substance which helps the body digest fat.
Gallbladder diseases such as cholelithiasis or cholecystitis are generally more common in post-menopausal women, and HRT is known to increase the risk.
The study, reported in the British Medical Journal, looked at a sample of more than one million post-menopausal women to see if any other factors influenced the likelihood of disease.
They found a total of nearly 20,000 women over a six-year period were admitted to hospital with gallbladder disease, and more than 17,000 of these had their gallbladder removed.
When rates of the illness among HRT users and women who did not use HRT were compared, the link between the hormones and the condition was confirmed.
However, hospital admission rates for patch-wearers were only 30% higher than for those who did not take HRT, while the rates for pill-users were roughly doubled, with two out of every 100 women taking oral HRT requiring gall-bladder removal.
The researchers suggested that the main reason for this was that while the hormone oestrogen taken in pill form is mostly broken down by the liver, next door to the gallbladder, before entering the circulation, the lower doses in the patch are absorbed directly through the skin into the bloodstream.
They calculated that, over a five-year period, if 140 women currently taking HRT pills switched over to patches, then this would mean one fewer gallbladder removal operation.
HRT use in the UK has fallen in recent years following evidence that, used in the long term, it raises the risk of breast cancer, although it is still recommended for the relief of menopausal symptoms over shorter periods.
Dr David Sturdee, from the International Menopause Society, said he was "surprised" by the high numbers of women found by the study to be suffering gallbladder problems. He said: "It's not a problem that many women are aware of."
He said that pills remained generally more popular among women: "Many opt for the pills because they are simpler, cheaper and because some women find that they cannot tolerate the patches due to skin irritation."