Seproxetine, also known as (S)-norfluoxetine, is a selective serotonin reuptake inhibitor (SSRI).

[1][2] It is the S enantiomer of norfluoxetine, the main active metabolite of the widely used antidepressant fluoxetine;[3] it is nearly 4 times more selective for stimulating neurosteroid synthesis relative to serotonin reuptake inhibition than fluoxetine.

[6] It was being investigated by Eli Lilly and Company as an antidepressant; however, it inhibited the KvLQT1 protein, which is responsible for the management of the QT interval.

Due to the inhibition, the QT interval was prolonged, which could lead to significant cardiac side complications.

[1] Tests on its efficacy found that it was equivalent to fluoxetine, but sixteen times more powerful than the R enantiomer of norfluoxetine.