Nagalati, 17, won a bronze medal in the pairs event at the Junior Grand Prix in Slovakia in September with skating partner Maxim Bobrov, but tested positive after the event for furosemide, a diuretic that can be used as a masking agent for other illegal substances.
Furosemide is banned by the World Anti-Doping Agency.
The International Skating Union said Nagalati admitted taking "one pill of furosemide following the advice of her mother's family doctor" for a health problem," unaware it is a banned substance. The Skating Union noted her story "appears to be credible."
Nagalati was assessed a one-year penalty instead of the standard two-year ban because of "her sincere confession," Russian Figure Skating federation Director Valentin Piseev told R-Sport, the sports department of the Russian news agency RIA Novosti.