What are the differences between fluoxetine and citalopram?

They are similar. Fluoxetine and citalopram are both selective serotonin reuptake inhibitors so they are in the same class of medicines. Fluoxetine is the oldest medicine in the class and has a long chemical half-life. Citalopram is much newer, has a shorter half-life and fewer side effects. They are both used to treat depression, anxiety and some other illnesses.
See below. They belong to the same class but have different side effect profiles and length of action inside the body. Citalopram http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0001041/ fluoxetine http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0000885/.