SSRIs typically dampen the effects of psychedelics, and Fluoxetine also has some activity as a 5HT2C antagonist (so it might potentially block psychedelics at that receptor subtype, although I'm not sure how high its binding affinity actually is)... still, 200µg of acid should have gotten you tripping unless you have serious tolerance or you were taking other drugs that antagonize serotonin receptors.
