What Is Depression? Symptoms, Causes, and Why Help Takes So Long

Depression often doesn’t feel like sadness. It can feel like moving through wet cement, losing interest in things you used to love, or lying awake at 3 a.m. wondering why everything takes so much effort. If that sounds familiar, you’re not lazy or weak, and you’re far from alone.

Your mood, motivation, sleep, and appetite are all regulated by connected networks in your brain and body. Depression disrupts several of those systems at once, which is why it can affect so much more than how you feel. Treating it well takes precision: matching the right care to the symptoms you actually have.

The established treatments are antidepressant medication and psychotherapy. A 522-trial network meta-analysis found that all 21 antidepressants studied worked better than placebo for adults with major depression. The results are real, and the science is well established.

But treatment only helps if it reaches you and stays with you, and at Siggy we don’t think anyone should spend years waiting for care that already exists. In a national U.S. survey, people with mood disorders who eventually sought treatment waited 6 to 8 years after their symptoms began.

This guide explains what depression is, how to recognize it, what causes it, how it’s treated, and why staying with treatment matters as much as starting. Understanding your depression is the first step toward care built on evidence.

What This Page Covers

• What Is Depression, Exactly?
• What Are the Symptoms of Depression?
• What Are the Different Types of Depression?
• What Causes Depression?
• How Is Depression Treated?
• Why Does Getting the Right Help Take So Long?
• How Siggy Fits In
• The Bottom Line on Depression
• Start Your Anonymous Intake

What Is Depression, Exactly?

Depression is a medical condition that changes how you feel, think, and function. Everyone has low days, and sadness after a loss or setback is a normal human response. Depression is different because it lingers, shows up most days, and spills into sleep, energy, concentration, and your ability to enjoy anything. Our guide to depression vs. sadness goes deeper on the difference.

It’s also very common. A national survey analysis of 2015 to 2020 data found that 9.2% of Americans age 12 and older had a major depressive episode in 2020, including 17.2% of young adults ages 18 to 25.

What Are the Symptoms of Depression?

Clinicians look at nine core symptoms. Under the standard diagnostic criteria, summarized in a 2016 clinical review, major depression means at least five of them, including low mood or loss of interest, most of the day, nearly every day, for at least two weeks. The symptoms also have to cause real distress or get in the way of work, relationships, or daily life, and a clinician checks that they aren’t caused by the effects of a substance or another medical condition.

• Persistent low, empty, or hopeless mood
• Loss of interest or pleasure in things you used to enjoy
• Changes in appetite or weight
• Sleeping too much or too little
• Fatigue or low energy
• Feeling worthless or excessively guilty
• Trouble concentrating or making decisions
• Moving or speaking more slowly, or feeling restless
• Thoughts of death or suicide

The PHQ-9 is a widely used questionnaire that scores each of those nine symptoms. In its original validation study of 6,000 patients, a score of 10 or higher identified major depression with 88% sensitivity and 88% specificity. The researchers set these severity bands.

PHQ-9 Score	Severity
0 to 4	None to minimal
5 to 9	Mild
10 to 14	Moderate
15 to 19	Moderately severe
20 to 27	Severe

A screening score isn’t a diagnosis, but it gives you and a clinician a shared starting point. Our guide to how doctors use the PHQ-9 explains what each range means for treatment, and our overview of signs of depression in adults covers how symptoms show up day to day.

What Are the Different Types of Depression?

Depression isn’t one-size-fits-all. The most common forms include:

• Major depressive disorder, with episodes of the symptoms above
• Persistent depressive disorder, a longer-lasting, lower-grade form
• Postpartum depression, which can develop during pregnancy or after giving birth
• Seasonal depression, which follows a seasonal pattern
• Bipolar depression, the low phase of bipolar disorder

The type matters because it shapes treatment. Bipolar depression in particular is treated differently, so it’s important to mention any past periods of unusually high energy or little need for sleep.

What Causes Depression?

There’s no single cause. Genes play a real but partial role: a twin-study meta-analysis estimated the heritability of major depression at about 37%, with the remaining risk largely tied to life experiences specific to each person.

You may have heard that depression is a chemical imbalance caused by low serotonin. A 2022 umbrella review found no consistent evidence that depression is caused by lowered serotonin, a conclusion other researchers argued was overstated in a published critique. Either way, antidepressants still outperform placebo in trials, which suggests they work through more complex brain changes than simply topping up one chemical.

For a deeper look at risk factors, read our guide to what causes depression.

How Is Depression Treated?

Most people do best with antidepressants, psychotherapy, or a combination. In the 522-trial analysis, every antidepressant beat placebo, though the effects were mostly modest and differences between drugs were small. Combining approaches adds more: a 2014 meta-analysis found that adding psychotherapy to antidepressants worked moderately better than medication alone for major depression.

Exercise belongs on the list too. A 2024 network meta-analysis of 218 studies found that walking or jogging, yoga, and strength training produced moderate reductions in depression, with bigger effects at higher intensity. Only one study was rated low risk of bias, so confidence in the exact size of the effect is low.

The right mix depends on how severe your symptoms are, what you’ve tried, and what fits your life. Our guide to medication vs. therapy for depression can help you weigh your options.

Why Does Getting the Right Help Take So Long?

Delays start before the first appointment. Beyond the years many people wait to seek care, the 2015 to 2020 survey analysis found that depression became more common without a matching rise in treatment, and help-seeking stayed consistently low.

Then comes the harder part: staying with treatment long enough for it to work and to keep working. Antidepressants usually take weeks, side effects can show up first, and once you feel better, stopping can seem reasonable. A 2003 Lancet review of 31 trials found that continuing antidepressants after improvement cut the odds of relapse by 70%, with average relapse rates of 18% on medication versus 41% after switching to placebo.

That’s why a medication that works on paper can fail in real life. No one checks in to see if it’s actually working, side effects go unaddressed, and a promising start quietly ends.

How Siggy Fits In

Siggy is built for the stretch where depression care usually falls apart. It starts with a free, anonymous intake, with no name or email required. A licensed prescriber reviews your intake before anything is prescribed, and you get a summary you can keep and share, so you don’t have to retell your story every time you see someone new.

Once you’re on a plan, Siggy is built to stay with you between appointments. Questions about side effects, doses, and whether it’s time to adjust have somewhere to go, and if you’re feeling better and thinking about stopping, your prescriber can help you decide when and how to taper safely.

Siggy’s licensed prescribers diagnose and treat the full range of mental health conditions, including depression and bipolar disorder, and Siggy combines human clinicians with AI therapy and daily check-ins. If your history suggests bipolar disorder or another condition, your prescriber reviews your full picture before making a diagnosis or adjusting your plan.

This article is for education and isn’t a substitute for care from a licensed clinician.

The Bottom Line on Depression

Depression is a common, treatable medical condition, and having it says nothing about your strength or character. It’s recognized by a pattern of symptoms lasting at least two weeks, it comes from a mix of genetic and life factors, and antidepressants, therapy, and exercise all have evidence behind them. The biggest risks are waiting too long to start and stopping too soon. If you’re still wondering whether what you feel counts, our guide to whether you might be depressed is a gentle place to start.

Start Your Anonymous Intake

If you’re having thoughts of suicide or harming yourself, call or text 988 now, or call 911 in an emergency. If depression has been weighing on you and you want a prescriber to look at the whole picture, start your anonymous intake. It’s free, there’s no name or email required, and a licensed prescriber reviews your intake before anything is prescribed. A real doctor reviews everything, and your summary is yours to keep.