A method for producing a microRNA target site blocking nucleic acid directed at a specific transcript, wherein the oligonucleotide sequence of the nucleic acid overlaps the 5' or 3' end of the microRNA target site, and at the same time partly overlaps the non-microRNA target sites, the method comprising the steps of: 1) selecting a known microRNA having at least one identified or putative microRNA target site, 2) obtaining the sequence of said microRNA and the sequence of one of said microRNA target sites, 3) selecting and obtaining the sequence of a transcript which comprises the microRNA target site selected in step 2, 4) designing a microRNA target site blocking nucleic acid which is at least 10 nucleotides long and comprises at least one LNA analogue and which is either a) at least partially complementary to the microRNA target site and which comprises a consecutive sequence of nucleotides which are complementary to the 3' end of the microRNA target site selected in step 3 and a consecutive sequence of nucleotides which are complementary to the transcript sequence immediately adjacent and downstream of the 3' end of the microRNA target site, or b) at least partially complementary to the microRNA target site and which comprises a consecutive sequence of nucleotides which are complementary to end 5' end of the microRNA target site selected in step 3 and a consecutive sequence of nucleotides which are complementary to the transcript sequence immediately adjacent and upstream of the 5' end of the microRNA target site 5) synthesizing the nucleic acid designed in step 4. 1) selecting a known microRNA having at least one identified or putative microRNA target site, 2) obtaining the sequence of said microRNA and the sequence of one of said microRNA target sites, 3) selecting and obtaining the sequence of a transcript which comprises the microRNA target site selected in step 2, 4) designing a microRNA target site blocking nucleic acid which is at least 10 nucleotides long and comprises at least one LNA analogue and which is either a) at least partially complementary to the microRNA target site and which comprises a consecutive sequence of nucleotides which are complementary to the 3' end of the microRNA target site selected in step 3 and a consecutive sequence of nucleotides which are complementary to the transcript sequence immediately adjacent and downstream of the 3' end of the microRNA target site, or b) at least partially complementary to the microRNA target site and which comprises a consecutive sequence of nucleotides which are complementary to end 5' end of the microRNA target site selected in step 3 and a consecutive sequence of nucleotides which are complementary to the transcript sequence immediately adjacent and upstream of the 5' end of the microRNA target site a) at least partially complementary to the microRNA target site and which comprises a consecutive sequence of nucleotides which are complementary to the 3' end of the microRNA target site selected in step 3 and a consecutive sequence of nucleotides which are complementary to the transcript sequence immediately adjacent and downstream of the 3' end of the microRNA target site, or b) at least partially complementary to the microRNA target site and which comprises a consecutive sequence of nucleotides which are complementary to end 5' end of the microRNA target site selected in step 3 and a consecutive sequence of nucleotides which are complementary to the transcript sequence immediately adjacent and upstream of the 5' end of the microRNA target site 5) synthesizing the nucleic acid designed in step 4.