The fine print at the bottom of prescription drug commercials may provide ample comedic firepower — what are they hiding?  — but underneath the humor lies a chilling reality: In their noble pursuit of making you healthy, prescription drugs put you at risk for a number of terrifying side effects, chief among them being antidepressants’ risk for suicide.

Where would we be without medication? The Centers for Disease Control and Prevention reports nearly half of the U.S. population has used at least one prescription drug within the last month, with drugs ordered or provided during physician office visits totaling 2.6 billion in 2010. Antidepressants alone, which have been derided as overprescribed, are used by more than 10 percent of the population 12 years and older. Among women in their forties and fifties, the rate jumps to 25 percent.

What Antidepressants Do

With all this in mind, it’s helpful to understand why we even take antidepressants in the first place. Most antidepressants, the big names like Prozac, Zoloft, and Celexa, are classified as selective serotonin reuptake inhibitors (SSRIs). These drugs work via the hormone serotonin, often referred to as the “happiness hormone,” to increase the levels in your brain by stopping (inhibiting) the absorption (reuptake) through the brain’s various receptors.

SSRIs don’t cure depression. They can only treat the symptoms, which, in this case, are hormonal imbalances. They’re also imperfect. Dr. Ann Blake Tracy, an expert on the flaws of drugs like Prozac and Zoloft, points out in her book Prozac: Panacea or Pandora? that “animal studies demonstrate that in the initial administration Prozac actually causes the brain to shut down its own production of serotonin, thereby causing a paradoxical effect or opposite effect on the level of serotonin.” The brain’s chemistry naturally wants to remain balanced, she adds, and any disruption from SSRIs or other medications throws that balance off.

What results from this volatility is something like a rollercoaster effect. A person’s mood goes from consistently depressed to temporarily content to all over the place very quickly. It’s for this reason the Food and Drug Administration requires “Black box warnings” on all SSRIs, stating explicitly that they double suicide rates from two per 1,000 to four per 1,000 in children and adolescents.

Another theory claims that antidepressants aren’t directly increasing a person’s risk at all. SSRIs endow depressed people with a newfound alertness and proactivity. If someone was suicidal before taking an antidepressant, but unmotivated to act on their urge, the antidepressant only facilitated their latent desires; it didn’t create them. In both cases, a 2004 study argues that it’s within the first nine days of taking antidepressants a person is most at-risk for suicidal thoughts or behaviors.

Paradoxical Reactions

In pharmacology, this overall effect is known as a “paradoxical reaction.” A specific medication was intended to treat one symptom, but ended up producing it in greater magnitude. Benzodiazepines, common psychoactive drugs used to relax muscles and quiet convulsions, are prone to producing the exact opposite effects. Antibiotics as well, which have been in greater circulation in recent years, have been known to produce the “Eagle effect” — a phenomenon named after Harry Eagle, the physician who first noticed that when bacteria are exposed to antibiotics for a long enough time, their population rates not only stabilize; they increase.

Paradoxical reactions have been observed in depression sufferers and also obsessive-compulsive disorder sufferers. A 1990 study showed 10- to 17-year-olds were compelled to self-harm following administration of fluoxetine (Prozac), leading to the hospitalization of four out of the 42.

And while certifiable advances have been made in the 24 years following the study, SSRIs continue to carry the warning. They have to: As long as the medication that’s designed to realign the juices in our brain that make us happy or depressed can turn against us, the threat of ending it all will always be lurking in the fine print.