Like-for-like sales at the British pharmacy chain tumbled 29% after COVID-19 impacted footfall, especially in major high street, train station and airport locations.
Market share was lower in all categories except beauty, as the pandemic continued to impact heavily on buying habits and consumers temporarily shifted purchasing to one-stop grocery shopping, the US company said.
Sales in the wider group were up 2% to US$34.7bn, while adjusted operating income decreased 28% to US$1.1bn.
Also on Thursday, Boots UK announced it is removing plastics from gift packaging to cut 2,020 tonnes of plastic from its Christmas gift ranges.
It also partnered with BBC Earth to launch a new eco-friendly gift collection for the festive season.
In July the company announced plans to cut 4,000 staff at Boots UK and permanently close 48 Boots Opticians.
Shares in Walgreens rose 1% to US$36.28 in premarket trading.