The day before the doping control, Llagostera Vives had visited San Francisco but said she had "only consumed a bottle of water" while there, the ruling stated.
ITF expert witness Christiane Ayotte said the banned substance "was and is available only as a street drug (crystal meth or meth) or as a stimulant or as a party drug," except when prescribed for some behavioral disorders.
The ruling stated that Llagostera Vives did not claim a medical exemption which would explain why the substance was present, and only later informed that she took some supplements and over-the-counter medications in the days before the doping control.
The tribunal panel expressed concern about how the ITF educated players in completing paperwork when asked to give samples.
"The main concern would be if the player's professed ignorance of the significance of completing this part of the form correctly and fully were to be attributable to a lack of education in this respect of Ms. Llagostera and her fellow professionals," the tribunal panel said.
Llagostera Vives will retain prize money and ranking points in five tournaments played since July, including reaching the last 16 in doubles at the U.S. Open together with Liezel Huber.