The similarly named Fluoxetine has lesser (but still significant) effects at Sigma-1. Since Fluoxetine is so widely distributed (because it's Prozac), there is quite a bit of observational data that Fluoxetine is also correlated with reduced clinical severity. Obviously, even a strong correlation is not causation but it is certainly grounds for prioritizing investigation, especially since Fluoxetine/Prozac is very well-tolerated, inexpensive and widely available in mass quantity.
Fluvoxamine has the highest sigma-1 affinity by far. Fluoxetine's affinity is about an order of magnitude lower.
We don't even know if sigma-1 is responsible for the effects observed, but it wouldn't make sense to give someone Fluoxetine instead of Fluvoxamine (which is also widely available), especially when it would require overdose levels of Fluoxetine to achieve similar sigma-1 effects.
