Men receiving the most common treatment for prostate cancer are 44 per cent more likely to develop diabetes, according to experts.
Scientists at the Harvard Medical School noticed that the side-effects of a gonadotropin-releasing hormone agonist drug, used in prostate cancer treatment, included a heightened risk of diabetes.
In addition, the drug increased the patients' risk of cardiovascular disease by 16 per cent.
Prostate cancer is the most common form of cancer in the UK, leading to around 10,000 deaths each year.
Study co-author Dr Matthew Smith said that the discovery could have implications for the drug's use in patients with prostate cancer.
"Doctors should think twice about prescribing agonists in situations for which studies have not demonstrated improved survival until we better understand the risks of treatment," Dr Smith said.
"For men who do require this treatment, physicians may want to talk with their patients about strategies, such as exercise and weight loss, which may help to lower risk of diabetes and heart disease," he added.
The research is due to be published in the Journal of Clinical Oncology.