Doctors most commonly prescribe SSRIs as the first medication for depression. These are a class of antidepressant that works by increasing serotonin activity in the brain, and they’ve been the standard starting point for over two decades because they’re effective for most people and cause fewer side effects than older options. If the first medication doesn’t work well enough, your doctor has several other classes to try, along with add-on treatments and non-medication options for harder-to-treat cases.
SSRIs: The Most Common Starting Point
Selective serotonin reuptake inhibitors are the first-line treatment for major depression. Among them, sertraline and escitalopram stand out in large analyses as having strong effectiveness with relatively mild side effects, which is why many doctors reach for one of these two first. But six SSRIs are widely prescribed, and the best choice depends on your specific symptoms, other medications you take, and how your body responds.
The SSRIs your doctor might prescribe include sertraline, escitalopram, fluoxetine, citalopram, paroxetine, and fluvoxamine. Each one works on the same brain chemical (serotonin) but differs slightly in how the body processes it, how long it stays active, and which side effects are most likely. Fluoxetine, for example, stays in your system much longer than others, which can be helpful if you occasionally miss a dose. Paroxetine tends to be more sedating, which some people find useful and others don’t.
Common side effects across all SSRIs include nausea, headaches, sleep changes, and sexual dysfunction. These effects are often strongest in the first week or two and then ease up. Weight changes can happen but vary from person to person and from drug to drug.
SNRIs: When SSRIs Aren’t Enough
If an SSRI doesn’t provide enough relief, doctors often turn to serotonin-norepinephrine reuptake inhibitors. These work on two brain chemicals instead of one, adding norepinephrine to the mix. That extra mechanism can help with fatigue, concentration problems, and the physical aches that sometimes accompany depression.
The most commonly prescribed SNRIs are venlafaxine and duloxetine. Duloxetine has a particularly broad range of uses: it’s also approved for generalized anxiety, nerve pain from diabetes, fibromyalgia, and chronic musculoskeletal pain. If your depression comes with significant physical pain or a co-existing pain condition, duloxetine may pull double duty. Desvenlafaxine and levomilnacipran are also available, though prescribed less often.
Side effects overlap with SSRIs (nausea, sexual dysfunction, sleep disruption), but SNRIs can also raise blood pressure slightly, so your doctor may monitor that.
Bupropion and Mirtazapine
Not every antidepressant fits neatly into the SSRI or SNRI category. The American Psychiatric Association’s treatment guidelines list bupropion and mirtazapine alongside SSRIs and SNRIs as optimal first choices for most patients, meaning your doctor might start with one of these instead, depending on your symptoms.
Bupropion works on dopamine and norepinephrine rather than serotonin. Its biggest practical advantage is that it rarely causes sexual side effects or weight gain, two of the most common reasons people stop taking other antidepressants. It can also help with low energy and motivation. On the flip side, it can increase anxiety and isn’t a great fit if anxiety is a major part of your depression picture.
Mirtazapine works differently from all the others. It tends to be sedating, which makes it useful when insomnia is a prominent symptom. It also stimulates appetite, so doctors sometimes choose it for people who’ve lost significant weight during a depressive episode. In comparative studies, mirtazapine caused fewer treatment dropouts than paroxetine, and some research suggests it starts working slightly faster than several SSRIs, with measurable improvement as early as the first week.
How Long Antidepressants Take to Work
One of the hardest parts of starting an antidepressant is the wait. Most people notice some improvement within one to two weeks, but this early change is often subtle. The average time for a meaningful antidepressant effect is about 13 days, while a full response typically takes closer to 20 days or more. Doctors generally recommend giving a medication at least four to six weeks at an adequate dose before deciding it isn’t working.
Some medications may produce noticeable changes sooner. In head-to-head comparisons, citalopram showed significantly reduced depression scores at week two compared to fluoxetine or sertraline. Mirtazapine also showed faster initial improvement than several SSRIs in early trials. But “faster” still means days to weeks, not hours. If you don’t feel different after the first few days, that’s completely expected.
When the First Medication Doesn’t Work
Roughly a third of people don’t respond adequately to their first antidepressant. When that happens, your doctor has several strategies: switching to a different medication, increasing the dose, or adding a second medication on top of the first.
Combination therapy can be effective. In one controlled trial, combining an SSRI with bupropion produced higher remission rates than either drug alone at the two-week mark. When patients who hadn’t improved on a single drug had a second medication added, about a third of them reached remission. Interestingly, switching medications entirely was less effective than adding a second one in the same study.
Three atypical antipsychotics, aripiprazole, quetiapine, and olanzapine, are FDA-approved specifically as add-on treatments when antidepressants alone aren’t enough. These are used at much lower doses than when treating psychotic disorders, and they can boost the effect of your antidepressant. They do carry their own side effects, including weight gain and metabolic changes, so doctors typically reserve them for cases where other combinations haven’t worked.
Options for Treatment-Resistant Depression
Depression that hasn’t responded to at least two adequate medication trials is classified as treatment-resistant. At this stage, additional options open up.
Esketamine nasal spray (brand name Spravato) is FDA-approved for treatment-resistant depression in adults. It works through a completely different brain pathway than traditional antidepressants, targeting the glutamate system. The catch is that it can’t be picked up at a pharmacy and used at home. You take it in a certified healthcare setting, under direct observation, and then stay for at least two hours of monitoring because it can cause sedation and a dissociative feeling. Patients and treatment facilities must both be enrolled in a special safety program. Despite the logistical burden, it offers a meaningful option for people who haven’t found relief elsewhere.
Transcranial magnetic stimulation (TMS) is a non-medication treatment that uses magnetic pulses to stimulate specific areas of the brain. It’s typically considered after multiple antidepressants have failed, and most insurance policies require documentation of those failed trials before covering it. Sessions are done in a clinic, usually daily for several weeks.
MAOIs: A Last Resort
Monoamine oxidase inhibitors are among the oldest antidepressants and can be remarkably effective for people who haven’t responded to anything else. They’re rarely prescribed first because they require strict dietary restrictions (certain aged and fermented foods can cause dangerous blood pressure spikes) and interact dangerously with many common medications. But the APA guidelines are clear that they should be considered when other treatments have failed.
The Black Box Warning on Suicide Risk
All antidepressants in the United States carry an FDA black box warning about the possibility of increased suicidal thoughts and behaviors in people under 25. This warning was first issued for children and adolescents in 2005 and expanded to include young adults in 2007. It doesn’t mean antidepressants cause suicide. It means that in clinical trials, a small number of younger patients experienced worsening suicidal thinking early in treatment, likely during the window before the medication’s full effect kicks in. For adults over 25, antidepressants are consistently associated with reduced suicide risk. Regardless of age, close monitoring in the first few weeks of treatment is standard practice.
What Your Doctor Considers When Choosing
There’s no blood test or scan that tells your doctor which antidepressant will work best for you. The decision is based on a combination of factors: your specific symptoms (insomnia vs. fatigue, anxiety vs. numbness, appetite loss vs. overeating), any co-existing conditions like chronic pain or anxiety disorders, side effects you most want to avoid, other medications you’re taking, and whether any close family members responded well to a particular drug.
If sexual side effects are a dealbreaker, bupropion or mirtazapine may be preferred over SSRIs. If you’re also dealing with chronic pain, duloxetine addresses both. If insomnia dominates the picture, mirtazapine’s sedating effect becomes an advantage. If you’ve been on an antidepressant before and it worked, most doctors will start there again. The process is often iterative, adjusting based on how you respond over weeks. That can feel frustrating, but each trial narrows the search and brings you closer to the right fit.