Sexual side effects usually last for the duration of taking Prozac, according to the National Alliance on Mental Illness. Most other Prozac side effects diminish after the first few weeks, as long as a patient takes Prozac as prescribed. As of 2015, there are no known problems with long-term use of the drug. However, serious side effects can occur with allergic reactions or drug interactions.
Common sexual side effects of Prozac use include difficulty orgasming or problems ejaculating. Decreased sexual desire is also one of the most common side effects of Prozac use, reports Everyday Health.
Women who take Prozac for long-term treatment for major depressive disorder and wish to conceive a child should discuss the side effects that Prozac causes while pregnant, states the National Alliance on Mental Illness. Prozac increases the risk of premature birth and infant pulmonary hypertension. However, untreated major depressive disorder also carries significant risks to both the mother and fetus, so a doctor may still recommend taking the drug while pregnant.
Weight gain may also be a long-term side effect of Prozac use, reports Everyday Health. One study found that people who took Prozac and other serotonin-specific reuptake inhibitors gained one to two pounds over the course of a year. Other research indicates that up to 25 percent of patients taking Prozac gained over 10 pounds, but conflicting research indicates that Prozac can cause some patients to lose weight.