Tymoshenko, a former revolutionary leader who served as prime minister from 2007-10, went on a hunger strike to protest what she said was a rigged parliamentary election.
Russia's state-run news agency RIA Novosti reports the penitentiary service in the former Soviet republic cited Ukrainian doctors as saying she was urged to end her protest.
Her lawyer, Serhiy Vlasenko, said Tymoshenko is in poor health.
Tymoshenko is serving a seven-year prison term after being convicted on corruption charges stemming from a 2009 natural gas deal with Russia's Gazprom. Tymoshenko's political supporters say the charges against her are politically motivated.
Her Fatherland Party came in second with 25.5 percent of the vote, losing to the ruling Party of Regions.
European observers to the October election said democracy in Ukraine took a step backward following the vote.