Unfortunately, one of the major and very common side effects of SSRIs is sexual dysfunction. Serotonin transmission also plays a role in the regulation of sexual responsiveness, and in ways we do not yet fully understand, when you block the re-uptake of serotonin and make more serotonin available to the nervous system, you also get a severe decrease in almost all aspects of sexual functioning. Libido or sexual drive can be reduced. It becomes more difficult to become sexually aroused. Women find that orgasms are diminished in frequency and intensity or disappear altogether.
Males have problems with erections and ejaculation.
It is a cruel irony that, as a woman's depression gets better and she starts to become interested in the world and in pleasurable activities again, her SSRI medication has wiped out her sexual responsiveness. Not all people get the sexual side effects, of course, but in my experience, most people do. To a certain extent, the sexual side effects are dose-dependent. This is for people whose moods are stable and who are good at monitoring themselves, and not for people who still have residual symptoms of depression. In contrast, the antidepressant effects are much longer lasting.