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Yes it can and this is typical of many of the Selective Serotonin Re uptake Inhibitors . However, there are certainly cases where these medications remain effective for specific individuals for many years and so it may just be that you are one of the lucky ones who doesn't experience the law of diminishing returns! We all metabolize medications in slightly different ways so while it's common to loose effect over time your situation is by no means unusual.
If you have further questions or would like to discuss this issue further please let me know. If not.....I wish you the best of luck!