The 21-year-old pop star set the record straight at a press conference at O2 Arena before she went onstage, reported E!Online.
"I didn't have a drug overdose. I took some antibiotics that a doctor gave me for a sinus infection and I had a reaction.
"I'm feeling good. I'm the poster child for good health. I've been laying down for three weeks. I'm gonna go offI'm like a star waiting to explode," she said.
She was out of the hospital on April 24, after which a brief setback kept her from traveling for a few extra days.
"I'm on this crazy vitamin rush and crazy honey and lavender. I learned a lot about taking care of yourself [while she was laid up]. I'm probably the only one on this tour who doesn't drink or smoke before a show, as I take this really seriously...," she added.