The 21-year-old pop star delayed her U.S. dates until August after treatment for a sinus infection went awry and last week postponed two European shows. Cyrus says she suffered a severe allergic reaction to antibiotics.
But she told reporters she was "the poster child for good health" before performing at London's O2 Arena on Tuesday.
"I've been laying down for three weeks. I'm gonna go off - I'm like a star waiting to explode," she said.
The former child star, who has garnered mixed reviews for her risque adult image, gave an energetic performance complete with crotch-grabbing, erotically tinged choreography and a ride on a giant hot dog.
Songs ranged from Cyrus' hits "We Can't Stop" and "Wrecking Ball" to covers of Bob Dylan's "When You Go" and Dolly Parton's "Jolene."