How do different SSRI medications work differently?

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There’s a ton of different SSRI’s (Cipralex, Zoloft, Prozac, Paxil, etc) and it’s widely known that people tend to respond better to one SSRI over another.

What confuses me is that SSRI’s all do the same thing on a physiological level, right? They all prevent the re-uptake of serotonin. Therefore, my understanding is they all work by increasing the person’s serotonin levels. So what makes some people respond better to one SSRI over another if they all do the exact same thing to your brain?

I understand why an SSRI might work better for somebody than a SNRI or MAOI, and it’s because they function differently and target different neurotransmitters. But why would one SSRI help somebody over another SSRI?

Help it make sense

In: 1

There are not really a “ton” of SSRI’s, there are only six currently available (some are not available in various countries), and 2 of them are closely related.

Although they all result in more or less the same result, a greater availability of serotonin, the exact mechanism of how they do it is different. The exact way in which they are processed by the body and affect reuptake is different. Think of it like a pitcher in baseball. The goal is to get the ball in to the glove of the catcher (ideally without the batter hitting it), but though the process is MOSTLY the same, there are differences in how each type of pitch is thrown. A curve ball and a sinker are not the same. But they can both achieve the same end goal.

Our understanding of neurochemistry and neuropharmacology is still, unfortunately, very limited. The reality is a lot of the details on how and why these drugs do what they do isn’t fully known. One of those mysteries is why individuals react so differently. Its not just which drug either, but dosage levels vary from person to person too.

Undoubtedly as we gain more knowledge and do more research into neurochemistry and neuropharmacology we’ll be able to improve our answers to these kind of questions.

Several factors. The drugs have differences in their structures, which will alter how they are absorbed, distributed and metallised in your body. People have slight variances in the enzymes and protein transporters, which will mean slight differences in how they react to drugs.

This is also true for the serotonin reuptake transporter itself. Slight variations in DNA will cause slight differences in the structure, which will affect how well different variations of SSRi’s are able to have their effect on them.

Even though they are called selective serotonin reuptake inhibitors, they aren’t entirely selective. They still have some effect on other receptors, just to a much smaller extent.