Amir Khan, a former light-welterweight world champion, has been handed a two-year ban from all sport.
He was banned after testing positive for a prohibited substance, UK Anti-Doping said on Tuesday.
Khan, 36, returned a positive result for the anabolic agent ostarine following his loss to Kell Brook in Manchester in February 2022.
Ostarine is a drug designed to have similar effects to testosterone.
Khan, who announced his retirement in May last year, accepted a violation of anti-doping rules but said he had not intentionally ingested the substance, an argument accepted by an independent panel following a hearing in January.
The ban is deemed to have commenced on 6 April 2022, when his provisional suspension was imposed, and will expire on 5 April 2024.