A luggage search showed nothing unusual. But a frisk by female officers revealed irregularities and deformations in both of the suspect's breasts.
The passenger then "became nervous and confessed to carrying cocaine implants", a police statement said on Friday.
The suspected drug smuggler was transferred to a hospital where she was detained for an alleged crime against public health, the statement says.
Spain employs a police unit to specifically check passenger arrivals from major drug-producing countries.