Is 10mg citalopram likely to cause weight gain?

Yes, it possible: Some people are sensitive to the weight gain side effects of Celexa (citalopram) even in small doses. Usually it is rare at this dose but not impossible. But before you do anything make sure the weight gain is related to celexa (citalopram). You could try the old method of controlling what you eat and exercise and see if you still gain weight, then you can talk to your psychiatrist looking for options.