Antidepressants: Types, How They Work, and What to Expect

The question most people ask when starting an antidepressant is: will this work? The question most prescribers wish patients would ask is: what should I expect in the next six weeks?

The gap between those two questions is where most antidepressant failures happen. Not because the medication was wrong. Because the first three weeks felt hard, and nobody had explained that was part of how it works.

This guide covers the practical reality of starting an antidepressant: what the different types do, what the evidence says about how well they work, what the first weeks actually feel like, and what adherence has to do with everything.

What This Page Covers

• Why antidepressants take weeks, not days, to work
• The main types and what makes each one different
• What 40 to 60% response rate actually means
• What to expect in the first two to eight weeks
• Early side effects that commonly drive premature discontinuation
• When to switch vs. when to wait
• Combination treatment: medication and therapy together
• How SiggyMD’s monitoring model addresses the adherence problem

Why Antidepressants Take Time to Work

This is the fact that most patients are not adequately prepared for, and it is why so many treatments fail before they have had a chance to succeed.

Antidepressants do not work by instantly adding serotonin to your brain. The initial increase in synaptic neurotransmitter availability is just the beginning. What actually produces the antidepressant effect is a cascade of slower neurobiological adaptations that follows: receptor desensitization, increased production of BDNF (brain-derived neurotrophic factor), restoration of neuroplasticity, and structural changes in the circuits involved in mood and emotional regulation.

It can often take several weeks of taking an antidepressant to experience an improvement in depression symptoms, and several months before you no longer feel depressed. This is not a failure of the medication. It is the biology of how antidepressants work.

This timeline has a critical clinical implication: stopping an antidepressant in the first two to three weeks, before the therapeutic cascade has had time to develop, means the medication never had a fair trial. Most early side effects resolve in that same window. The patient who stops at week two is experiencing the cost without the benefit.

The Main Types of Antidepressants

SSRIs: The Default First Prescription

Selective serotonin reuptake inhibitors are the most commonly prescribed antidepressants. They work by blocking the transporter that removes serotonin from the synapse, increasing serotonin availability. SSRIs are the most prescribed type of antidepressant. They work by increasing levels of serotonin in the brain. They generally have fewer side effects than other types of antidepressants.

The reason SSRIs are first-line is not that they work better than other classes. It is that their side effect profile is more tolerable at standard doses, which improves the probability that patients will complete an adequate trial.

Common SSRIs include sertraline (Zoloft), escitalopram (Lexapro), fluoxetine (Prozac), paroxetine (Paxil), and citalopram (Celexa). Each has slightly different tolerability and drug interaction profiles, which informs prescriber choice for individual patients.

SNRIs: When Norepinephrine Matters

Serotonin-norepinephrine reuptake inhibitors block the reuptake of both serotonin and norepinephrine. The broader mechanism makes them particularly useful for patients with co-occurring anxiety, chronic pain, or fatigue.

SNRIs are similar to SSRIs, differing mainly in their mechanism of action: they increase serotonin, but they also increase norepinephrine. Common SNRIs include venlafaxine (Effexor), duloxetine (Cymbalta), and desvenlafaxine (Pristiq). Duloxetine is FDA-approved for both depression and several pain conditions, including fibromyalgia and diabetic neuropathy, which makes it particularly useful when both conditions co-occur.

NDRIs: The Option Without Sexual Side Effects

Norepinephrine-dopamine reuptake inhibitors block reuptake of norepinephrine and dopamine without significantly affecting serotonin. Bupropion (Wellbutrin) is the primary example.

Bupropion’s different mechanism produces a different side effect profile: no sexual dysfunction, no weight gain, and an activating rather than sedating effect. It is also FDA-approved for smoking cessation. It is contraindicated in patients with seizure disorders or eating disorders.

Atypicals: When a Different Profile Is Needed

Atypical antidepressants cover a range of mechanisms that do not fit neatly into the above categories. Atypical antidepressants work differently than SSRIs and SNRIs. They may be prescribed when other types of medications do not work or cause unwanted side effects.

Mirtazapine (Remeron) is sedating and appetite-stimulating, useful for patients whose depression comes with insomnia and weight loss. It does not cause sexual dysfunction. Trazodone is commonly used in low doses for sleep. Vortioxetine (Trintellix) combines SSRI-like activity with direct serotonin receptor activity and is associated with cognitive benefits in some studies.

TCAs and MAOIs: Effective but Reserved for Later

Tricyclic antidepressants and monoamine oxidase inhibitors were the first antidepressants developed, and they are effective, sometimes very effective, for severe or treatment-resistant depression. But they carry heavier side effect burdens and, in the case of MAOIs, dangerous dietary and drug interactions.

MAOIs are not recognized as first-line treatment for depression because of the adverse effects and drug-drug interactions. These classes are typically reached after SSRIs, SNRIs, and atypicals have been tried.

Newer Agents

Esketamine (Spravato) targets the glutamate system through NMDA receptor antagonism and produces antidepressant effects within hours. It is FDA-approved for treatment-resistant depression and is administered in certified clinical settings. Zuranolone (Zurzuvae), FDA-approved in 2024, targets GABA-A receptors and is specifically approved for major depressive disorder and postpartum depression.

These are not replacements for SSRIs. They are options for patients who have not responded to conventional treatment.

What the Evidence Says: Response Rates in Plain Language

According to the Institute for Quality and Efficiency in Health Care, 40 to 60% of people who took an SSRI or SNRI for depression noticed some symptom relief within 6 to 8 weeks.

What does 40 to 60% response rate mean in practice? It means that for any individual starting an SSRI, there is roughly an even chance the first medication will produce meaningful symptom relief. The other 40 to 60% will need to try a different medication, a higher dose, or an augmentation strategy.

This is not a pessimistic statistic. It is a clinical reality that shapes the management of depression: starting an antidepressant is the beginning of a process, not a single decision. Finding the right medication at the right dose for a particular patient frequently requires more than one trial.

The STAR*D trial, the largest antidepressant effectiveness study ever conducted, found that cumulative remission rates improved with each successive medication trial: approximately 37% achieved remission on the first medication, and the cumulative rate approached 70% after multiple trials. The message is that persistence matters more than finding the perfect first choice.

What to Expect: The First Eight Weeks

Weeks 1 to 2. The most common early side effects appear: nausea, headache, jitteriness, diarrhea, or insomnia. Most of these problems may naturally go away as your body adjusts to the medicine. Some patients notice small improvements in sleep or energy before any mood change. Anxiety may temporarily worsen before it improves, particularly with SSRIs.

Weeks 3 to 4. Early side effects are typically resolving. Some patients begin noticing mood stabilization. For most, this is the window where discontinuation happens if no one has prepared them to expect that improvement comes later.

Weeks 6 to 8. Full antidepressant effect, if it is going to occur, typically becomes apparent here. This is the appropriate time to evaluate whether the medication is working, with your prescriber, based on standardized symptom tracking.

After 8 weeks at therapeutic dose. If there is no meaningful improvement, the trial is adequate and a different approach is warranted: dose adjustment, medication switch, or augmentation.

Why People Stop Too Soon, and the Clinical Cost

Antidepressant adherence is one of the most significant factors in whether treatment succeeds. One study found that 42% of patients with major depression discontinued antidepressants within the first month, and 72% discontinued within three months. Most of those who stopped did so before completing an adequate trial.

The reasons people stop matter clinically. Early side effects that feel discouraging but would have resolved. A sense that “this isn’t doing anything” at week two, before the therapeutic effects have developed. Sexual side effects that were not disclosed and therefore not addressed.

Every early discontinuation before an adequate trial is a medication that could have worked but was not given the chance. The clinical cost accumulates in the form of repeat episodes, progressive severity, and eventual treatment resistance.

This is precisely why continuous monitoring between appointments changes outcomes. A prescriber who knows at week two that a patient is nauseous and considering stopping can intervene: explain that nausea from SSRIs typically resolves by week four, suggest taking the medication with food, and keep the patient on track through the adjustment period.

Combination Treatment: Why Therapy Alongside Medication Matters

In many cases, combining an antidepressant with talk therapy, called psychotherapy, is more effective than taking an antidepressant alone.

The mechanism makes clinical sense. Antidepressants create the neurobiological conditions, improved neuroplasticity, reduced symptom burden, better sleep and concentration, in which therapeutic work becomes possible. Psychotherapy, particularly CBT and behavioral activation, addresses the thought patterns and behavioral habits that sustain depression and contribute to relapse. Neither alone addresses both dimensions.

For mild to moderate depression, therapy alone can be sufficient. For moderate to severe depression, medication is typically necessary to get symptoms to a level where meaningful therapeutic work can proceed. The most durable outcomes tend to come from patients who do both.

About SiggyMD

The most important variable in antidepressant success is not which medication you start. It is whether you stay on it long enough, at the right dose, with the right monitoring, to give it a fair chance.

SiggyMD’s daily check-in model changes what is visible to your prescriber. Instead of reconstructing the first eight weeks from memory at a quarterly appointment, your prescriber can see your symptom trajectory, side effect reports, and sleep patterns as they develop, adjusting in real time rather than after the fact.

“The first six weeks of an antidepressant are where most treatment relationships succeed or fail,” says Daniel Montville, MD, Psychiatrist at SiggyMD. “Not because the medication failed, but because nobody was watching closely enough to catch the early side effects that drive people to stop. That is what the check-in data does: it brings that window into view so we can keep the treatment on track.”

The anonymous intake requires no name, email, or account. A licensed prescriber reviews every treatment plan before anything moves forward.

For more on specific antidepressants, see our post on how doctors decide when a first-line antidepressant is not working, our guide to Lexapro for anxiety, and our guide to mirtazapine for anxiety. For insight on managing early side effects, see doctor explains antidepressants in the first 8 weeks.

Start your anonymous intake with SiggyMD to get a clinician-reviewed medication plan with continuous monitoring that keeps treatment on track.

What Members Are Saying

DH

D.H., 29

Major Depressive Disorder

“I stopped my first antidepressant at day 12 because I felt worse and figured it was not working. My prescriber at SiggyMD told me afterwards that what I had experienced was a typical early adjustment effect and the medication very likely would have worked if I had pushed through those two weeks. That information earlier would have changed what I did.”

ST

S.T., 43

Depression and Anxiety

“I had been on an SSRI for six years and it had stopped working. My previous prescriber just kept renewing the same prescription. SiggyMD’s intake process asked specifically about when I had last felt like the medication was working and what had changed. That structured review led to trying a different class. I had not realized there were this many options.”

Member stories reflect real experiences. Names and identifying details have been changed to protect privacy. Results vary. You can begin anonymous intake without an account, name, email, or payment.

Sources

1. Mayo Clinic. Antidepressants: Selecting one that’s right for you. Last updated September 2022.

2. NIH MedlinePlus. Commonly prescribed antidepressants and how they work. Updated August 2023.

3. HelpGuide. Antidepressant Medication. Accessed June 2026.

4. StatPearls. Antidepressants. NCBI Bookshelf; 2024.

5. Medical News Today. Antidepressants: Types, side effects, uses, and effectiveness. Updated January 2024.

6. Trivedi MH, et al. Evaluation of outcomes with citalopram for depression using measurement-based care in STAR*D: implications for clinical practice. American Journal of Psychiatry. 2006;163(1):28-40.

7. Cleveland Clinic. Antidepressants: What They Are, Uses, Side Effects and Types. Last updated August 2025.

8. Mayo Clinic. Adjusting your depression treatment. Accessed June 2026.