Former heavyweight world champion Joshua beat stand-in Helenius with a seventh-round single-punch knockout at the London O2 Arena.
But Helenius's sample from a voluntary drug test the day before the bout tested positive for clomifene, which the Finnish boxer said may have originated from consuming eggs and chicken.
Helenius, now 40, was provisionally suspended and UKAD said he was unable to provide proof that "the eggs and chicken meat he had consumed in advance of the bout originated from hens that had been administered clomifene".
"Mr Helenius was therefore unable to identify the source of clomifene in his sample and therefore unable to reduce the applicable period of ineligibility of two years," UKAD added.
However, UKAD said that since Helenius was provisionally suspended on September 18th, 2023, he has already served 10 months of his ban which will expire on September 17th, 2025.
