About Citalopram Selective Serotonin Reuptake Inhibitor (SSRIs), Antidepressant. Mechanism of Action of Citalopram Citalopram blocks the re-uptake of neurotransmitter Serotonin from the synapse to the presynaptic nerve terminal in the CNS. This potentiates the action of Serotonin (5HT) and it is useful in the treatment of depression. Indications for Citalopram Depression. Contra-indications of Citalopram 1.Hypersensitivity to Citalopram, 2.Patient on MAOI (Monoamine oxidase inhibitor) therapy. Special Precautions while taking Citalopram