Research from Kantar Worldwide suggests 23.2 million packs were sold in the year ending October 2016.
In the same timeframe in 2012, more than 29.4 million boxes of tampons were bought in the UK.
A million fewer packets of sanitary towels were also sold last year, compared to 2012, with total pack sales of 84.5 million.
In terms of cash, £236m was spent in 2012 on tampons, liners and sanitary towels.
Tampon sales account for £55.6m of that figure.
That compares to £221m in total and £43m on tampons in 2016.