Eleven percent of Americans aged 12 years and over take an antidepressant medication, according to the Centers for Disease Control and Prevention.

The use of antidepressants increased nearly 400 percent between 1988 and 2008. SSRIs are the most common class of antidepressants in the U.S. and are believed to be safer and generally cause fewer side effects than other antidepressants.

SSRIs are prescribed to treat depression, anxiety disorders, panic attacks and personality disorders. They have been shown to be more effective in severe cases of depression than in mild cases.

Before taking any prescription medication as directed by your doctor, it is important to ask the prescribing doctor questions about the treatment and its pros and cons. Below are some of the frequently asked questions about SSRIs.

Doctors are more likely to prescribe SSRIs to women. One in four women in their 40s and 50s take antidepressants, and 13 percent of pregnant women take these drugs.

There are several reasons why doctors prescribe SSRIs. Some are for uses not approved by the U.S. Food and Drug Administration, known as off-label uses.

Nerve cells in our brain use various chemicals to pass on impulses. SSRIs work by increasing the levels of a brain chemical called serotonin, which plays a key role in mood. The body naturally produces serotonin and keeps it at a certain level, but SSRIs can increase that level by blocking (inhibiting) the re-absorption (reuptake) of serotonin.

SSRIs are usually the first choice for doctors treating depression or anxiety with prescription medications, but they’re not for everyone. It is normal to feel sad or “down” in the wake of stressful life events such as the death of a loved one, a job loss or a divorce. These feelings should ease or subside on their own. Patients may be candidates for antidepressants if they aren’t functioning well, if the symptoms last for several weeks without getting better, or if there is no apparent reason for the symptoms. This is especially true if patients have a history of depression.

Many SSRIs are only FDA approved for use in adults but can be legally prescribed to treat depression or obsessive-compulsive disorder in children and adolescents. Prozac (fluoxetine) is the only FDA-approved medication for treating depression in children 8 and older, while Lexapro (escitalopram) is approved for children 12 to 17. Prozac, Zoloft (sertraline) and Luvox (fluvoxamine maleate) are approved for use in children and adolescents for the treatment of obsessive-compulsive disorder. Other SSRIs are not approved for use in children, but that does not mean a doctor can’t prescribe them as an off-label use for treating depression or anxiety disorders in patients under 18.

SSRIs are usually taken daily. The goal is to ease or eliminate the symptoms within the first few weeks to months. Treatment duration depends on several factors, including the severity of the symptoms and how well each individual responds to treatments.

Most patients take SSRIs for several months, but some may require years of treatment. According to the CDC, 14 percent of Americans taking antidepressants have done so for 10 years or longer. The duration also depends on the chance of relapse. Patients with a history of depression or those going through a traumatic life event may experience a relapse of major depression. A relapse may also occur if a patient suddenly stops taking an SSRI (discontinuation) or if their dosage is significantly reduced.

It’s difficult to pinpoint the effectiveness of SSRIs because each individual and case is unique. Our bodies respond to medications in different ways. Doctors may end up prescribing a number of different SSRIs and dosage options before a patient finds one that works. In general, the effectiveness is usually tied to the severity of the depression or anxiety disorder.

According to a 2017 study from the Institute for Quality and Efficiency in Health Care, about 40 to 60 out of 100 people who took an antidepressant noticed an improvement in their symptoms within six to eight weeks. Typically, someone with an anxiety disorder such as obsessive-compulsive disorder (OCD) or generalized anxiety disorder (GAD) may see improvements faster compared to patients with severe depression.

SSRIs can range from about $21 a month (sometimes less) for generic versions to several hundred dollars a month for certain brand name drugs, according to a study from Consumer Reports. Generic versions are available for all SSRIs on the market, including Prozac, Paxil, Zoloft and Lexapro.

Although all SSRI drugs have the same mechanism of action — increasing serotonin levels in the brain — all SSRIs are not the same.

Each has slightly different pharmacological and pharmacokinetic characteristics, along with varying molecular structures. In other words, each drug has its own active ingredient with the same goal in mind.

These differences can be clinically significant, leading to variances in recommended dosage, common side effects, half-life (time required for the concentration of the drug in the body to decrease by half), effectiveness (including typical treatment duration) and potential drug interactions.

SSRIs have a number of common side effects, including fatigue, weight loss, apathy, insomnia, headaches, nausea and pupil dilation. They are also linked to sexual side effects such as repressed libido, erectile dysfunction (impotence) for men and difficulty achieving orgasm for men and women.

Side effects are more common with higher doses and are likely to improve or go away completely once the body adjusts to the medication. However, SSRI use can also lead to serious side effects, some of which are life-threatening.

Patients taking SSRIs have a reduced capacity for their blood to clot. A lower concentration of serotonin in platelets increases the risk for stomach or uterine bleeding, which means an increased need for a blood transfusion during or after surgery.

This condition is a drop in a person’s sodium levels, which can lead to the accumulation of fluid in cells and is dangerous. Elderly people especially should be monitored for this condition from the beginning of treatment.

Another serious concern for SSRI patients is whether they will suffer withdrawal symptoms when they stop taking the antidepressants.

SSRIs technically are not considered addictive because they do not cause cravings in the body when the patient stops taking the drugs. However, studies show that the antidepressants can make users dependent on the drugs, and patients can suffer withdrawal symptoms.

Drug dependency is the state where a person needs steady or increasing doses of the drug to maintain normal functioning. Patients are warned not to stop taking SSRIs suddenly because they may experience withdrawal side effects.

In severe cases, patients will have a collection of symptoms called SSRI Discontinuation syndrome, which can last up to several weeks.

All SSRIs carry an FDA black box warning — the agency’s most stringent precaution — for an increased risk of suicidal thoughts and behaviors (suicidality) in adults and children 24 and younger.

Only Prozac and Lexapro are FDA-approved for treating depression in children, while Prozac, Zoloft and Luvox are approved for treating children and adolescents with obsessive compulsive disorder. However, all SSRIs can be prescribed to children and teens as an off-label treatment for depression and anxiety disorders.

Unfortunately, this may have resulted in more suicide attempts among youth who needed antidepressants but did not take them because of the warning. A study found that antidepressant use in adolescents dropped 31 percent after the FDA issued the black box warning, but suicide attempts among youth increased 22 percent.

Parents and caregivers of children being treated for depression with SSRIs should watch for worsening irritability, nervousness, agitation, mood instability or sleeplessness.

Suicidal thoughts and behaviors are the most common symptoms of major depression for all ages. Doctors and their patients should carefully weigh the risks with the benefits when prescribing SSRIs to treat depression.

The FDA cautions women about the use of SSRI antidepressants during pregnancy.

One way the agency has conveyed this warning is with letter grades, or categories, that are assigned to prescription medications to denote their safety ratings. Most SSRIs are Category C, meaning they have been known to harm laboratory animals when they ingested the drugs in large quantities.

Paxil is the one exception. The drug and its generic form (paroxetine) carry a Category D warning, which means that there is “positive evidence of human fetal risk based on adverse reaction data from investigational or marketing experience or studies in humans.”

Zoloft and Prozac are the two most common SSRIs prescribed to pregnant women, but Paxil or any other SSRI can be prescribed if doctors think the benefits of the medication outweigh the potential risks. Untreated depression in pregnant women can also lead to serious complications, including continued depression after delivery (postpartum depression) and even the potential of pregnancy termination or suicide.

There has been a series of conflicting studies in recent years regarding the association of SSRI drugs and birth defects. A comprehensive study from the National Center on Birth Defects and Developmental Disabilities revealed that the most common reported links include heart, brain and abdominal birth defects.

Some researchers suggest that it is too difficult to quantify the risk of SSRIs during pregnancy because untreated depression and anxiety disorders can also lead to birth defects and an increased risk of a child developing autism.

Drug manufacturers have paid billions in government fines, class-action settlements and lawsuit verdicts over potential dangers of SSRI medications. Some notable ones include:

SSRIs are considered second-generation antidepressants and are often prescribed to treat depression before other types of antidepressants, including serotonin and noradrenaline reuptake inhibitors (SNRIs) and tricyclic antidepressants (TCAs).

SSRIs can improve the symptoms of depression, but they can also cause serious side effects. A 2014 study from researchers at the Nordic Cochrane Centre and the University of Copenhagen found that patients who were given antidepressants but were not truly clinically depressed had a higher risk of suicidal thoughts or behaviors while using the medications.

The Danish researchers suggest that many of the prescriptions were given “unnecessarily” as an alternative to other treatment options, including therapy. SSRIs should only be taken if the patient and their doctor or mental health professional believe it is the best possible option for treating severe depression or a serious anxiety disorder.

Serotonin and noradrenaline reuptake inhibitors (SNRIs) work similarly to SSRIs, but instead of increasing only serotonin levels, SNRIs also increase the amount of noradrenaline, a hormone that produces a wide range of effects on the body.

By increasing noradrenaline levels, brain cells seem to communicate better, which can boost a person’s mood.

However, SNRIs may decrease libido, cause weight gain and increase fatigue and drowsiness. More serious side effects include birth defects in pregnant women and a risk of withdrawal from discontinuation.

Tricyclic antidepressants (TCAs) are an older class of antidepressants, having been available for more than 50 years. They can be as effective as newer antidepressants, but they usually carry more side effects, including dizziness, constipation and dry mouth. TCAs might be prescribed if other antidepressants are proven ineffective.

The most common alternative is therapy, which helps a person cope with feelings of hopelessness or anxiety. Cognitive behavioral therapy is a type of psychotherapy in which negative patterns of thought are challenged in order to change unwanted behavior patterns.

A 2012 study published in The Lancet discovered that nearly half of patients who had depression and were resistant to antidepressant medications benefited from cognitive behavioral therapy. Therapy can also be an effective option for women with depression who don’t want to risk taking antidepressant drugs while pregnant.

These options may not completely eliminate a person’s depression, but could relieve symptoms, lessening the need for SSRIs or other prescription antidepressants. A doctor or mental health professional can help navigate the process and decide which option or options might be rightfor each individual.