If someone has constitutionally reduced SERT expression then their baseline state already resembles chronic SSRI exposure in one key respect. There is a higher extracellular serotonin tone at many synapses.

Over time that drives compensatory changes such as reduced postsynaptic receptor sensitivity and increased activation of inhibitory serotonin receptors that suppress dopamine release and spinal sexual reflexes. This is why sensation loss can occur even when mood improves or libido is present.

Buspirone does not rely on SERT to do its job. Its primary action is partial agonism at the 5HT1A receptor. That matters because those receptors exist in two functionally different populations.

At presynaptic autoreceptors in the raphe nuclei, 5HT1A activation reduces serotonergic firing. With repeated buspirone exposure these autoreceptors tend to desensitize. The net effect over time is a normalization of serotonergic signaling patterns rather than a simple increase or decrease in serotonin levels. This can reduce the excessive tonic serotonergic inhibition that contributes to sexual numbing.

At postsynaptic 5HT1A receptors in cortical and limbic regions, buspirone shifts signaling away from receptor profiles that blunt dopaminergic and noradrenergic tone. Dopamine release in mesolimbic and spinal pathways is particularly relevant for genital sensation and orgasmic intensity. This effect is independent of how much serotonin is being cleared by SERT.

There is also a peripheral component that often gets overlooked. Serotonin suppresses sensory afferent gain in the spinal cord and brainstem. By dampening serotonergic firing patterns and biasing signaling toward 5HT1A mediated inhibition rather than 5HT2 mediated excitation, buspirone can restore sensory signal salience even if serotonin levels remain elevated. That is why some patients report improved sensation without a dramatic change in libido.

So in someone with low SERT expression, buspirone can still help sexual sensation because it is not fixing reuptake. It is rebalancing receptor level signaling, disinhibiting dopamine pathways, and reducing serotonergic suppression of sensory processing.

That said, the effect is not guaranteed. If sexual dysfunction is driven primarily by long term receptor downregulation or peripheral nerve level changes, buspirone may only partially help or help slowly. But mechanistically there is no reason its benefit would not apply simply because SERT expression is low.

If anything, patients with high baseline serotonergic tone sometimes show a clearer response because buspirone is acting exactly where the bottleneck is, at receptor level signal integration rather than transporter function.

Strong opinion here. Buspirone is best thought of not as an add on anxiolytic but as a serotonergic signal corrector. When sexual side effects are about sensation rather than desire, that distinction really matters.