The present invention relates to a pure 5-HT6 receptor antagonist selected from 1-[(2-Bromophenyl)sulfonyl]-5-methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole, 1-[(4-Fluorophenyl)sulfonyl]-5-methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole and 1-[(4-Isopropylphenyl)sulfonyl]-5-methoxy-3-[(4-methyl-1-piperazinyl)methyl]-1H-indole, or a pharmaceutically acceptable salt thereof, in combination with an acetylcholinesterase inhibitor and an N-Methyl-D-aspartate (NMDA) receptor antagonist, and their use in the treatment of cognitive disorders. The present invention further provides the pharmaceutical composition containing said combination and the use of the combination in an improved combination therapy for the treatment of cognitive disorders, such as Alzheimer’s disease, schizophrenia, Parkinson’s disease, Lewy body dementia, vascular dementia or frontotemporal dementia.
