That’s how the class came to be known as “selective serotonin reuptake inhibitors” they prevent (inhibit) serotonin (and only serotonin) from experiencing too much or too long of a reuptake process. This makes more serotonin available in the brain and thus raising the mood .
ususally SSRI are prescribed commonly and better to be taken by doctor prescription to adjust dosage and duration .
from what you had mentioned prozac ,zoloft ,and cipralex are SSRI sand they are safe but check as i said by your doctor ,sometimes everyone case is unique and the medicine or that work better on a specific case ,usually if a medication doesn't have an effect a doctor can merge to another until results seen or increase doses ,sometimes combined therapy are used to treat stubborn depression or somehow .
so check with a doctor and see what your case suits better