The invention provides pharmaceutical compositions comprising short single stranded oligonucleotides, of length of between 8 and 26 nucleobases which are complementary to human microRNAs selected from the group consisting of miR19b, miR21, miR122a, miR155 and miR375. The short oligonucleotides are particularly effective at alleviating miRNA repression in vivo. It is found that the incorporation of high affinity nucleotide analogues into the oligonucleotides results in highly effective anti-microRNA molecules which appear to function via the formation of almost irreversible duplexes with the miRNA target, rather than RNA cleavage based mechanisms, such as mechanisms associated with RNaseH or RISC.
