Serotonin reuptake inhibitors (SRI) can be defined as a sub class of the antidepressant medication family. They increase the net serotonergic neurotransmission in the brain which is a neurotransmitter by inhibition of the reuptake of serotonin (5-HT). In this way, the serotonins will not be reabsorbed in the brain and their levels will be increased. As a result of increase serotonin activity in the brain, the symptoms of depression would be decrease.

I am pleased to send you this link about the Therapeutic Effects of Serotonin Reuptake Inhibitors: The Role of 5-HT2 Receptors. In this article, it has showed the therapeutic mechanisms of the serotonin reuptake inhibiting drugs and their efficiency for several psychiatric conditions.

http://ki.se/content/1/c6/03/10/61/5Landen06PsyBull.pdf

I would just reiterate what Yanick Simon has said that any chemical that selectively inhibits the reuptake of the serotonin in the synaptic cleft is called SSRI and as a result of this inhibition of reuptake the level of serotonin increases.

This increase in serotonin has been linked with improved mood and alleviation of depressive symptoms as well as in the treatment of anxiety and OCD. However, the time taken by SSRI to show therapeutic effect is around 4 to 6 weeks whereas the increase in serotonin level is observed quickly. Such, observation puts a caveat against the theory that increase in the level of serotonin improves depression or brings other therapeutic effects.

Thus, the mechanism of action of the SSRI is still a research issue and several alternatives have been proposed such as change in the density of serotonin receptors, enhanced neurogenesis in the hippocampus etc. (all of which are observed after at least 4 to 6 weeks of SSRI administration).

Thank you Yanick Simon and Rakesh for your posts and useful details. could you please further explain that wither SRI and SSRI are similar or different?

They are the same group of medication. The serotonin reuptake inhibitors is nonselective it affects serotonin and other neurotransmitters. However the selective serotonin reuptake inhibitors primarily affect only serotonin such as fluoxetine, sertraline. The word nonselective serotonin reuptake inhibitors is often use than SRI.

The other thing to be aware of is how responsive and adaptive the monoamine system is. Any chemical that inhibits re-uptake of serotonin, and/or dopamine, and/or noradrenaline, and that is administered chronically, will eventually lead to neuroadaption (down regulation of natural release of these neurotransmitters, and/or de-sensitisation of receptors for these neurotransmitters).

This is why many clinically depressed patients prescribed Prozac or similar drugs initially report a great improvement in their symptoms, (after a week or two to allow the serotonin levels to increase) but three or four months later are reporting less significant, or no, improvements in mood.

Paul.

thanks Paul

SSRI's should not be used in patients taking Tamoxifen for breast cancer. While it is understandable that breast cancer patients may suffer from anxiety and depression the SSRI's interfere with the CYP450 enzymes responsible for metabolising Tamoxifen and reduce its potency significantly.