Benzodiazepines, which are taken by 2% of the population in the UK, have been associated with an increased risk of developing and dying from pneumonia.
Researchers say the medication, which is also taken for anxiety, epilepsy, insomnia and alcohol withdrawal, is associated with a 54% increased risk of developing the condition.
The drugs are widely used in many countries. In the UK it is estimated that up to one in 10 elderly people take them. Many administer the treatment for long periods despite guidelines suggesting it should only be used for a few weeks.
The research authors say the findings do not prove cause and effect, but suggest there could be grounds for further investigation.