What is depression?
Depression is not just feeling blue or a lack of willpower. It's a recognized medical condition — a neurobiological imbalance that affects your mood, energy, and ability to function daily. And most importantly: it can be treated.
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Depression is a mood disorder characterized by persistent sadness and loss of interest lasting at least 2 weeks. It affects 15 to 20% of the population over a lifetime (Inserm). It's not weakness — it's a dysfunction that can be treated in nearly 70% of cases.
En 30 secondes
Depression is recognized by the WHO and DSM-5 as a genuine medical condition. It involves an imbalance of neurotransmitters (serotonin, dopamine, norepinephrine) that affects mood, energy, sleep, and the ability to feel pleasure.
- 15 to 20% of the population affected in their lifetime (Inserm)
- Treatment effective in approximately 70% of cases (Inserm)
- Assessed using DSM-5 criteria and the PHQ-9 scale
What exactly is depression?
Depression — or major depressive episode — is a mood disorder that goes far beyond ordinary sadness. To be diagnosed according to the DSM-5, it requires at least 5 symptoms (including either depressed mood or loss of interest) present daily for at least 2 weeks, with significant impact on personal, social, or professional functioning.
At a neurobiological level, depression involves an imbalance of neurotransmitters — primarily serotonin, dopamine, and norepinephrine. But recent research (Inserm) shows the mechanism is more complex: the stress axis (HPA axis) is disrupted, cortisol is elevated, and neuroplasticity is impaired, reducing the brain's ability to adapt and produce BDNF (brain-derived neurotrophic factor).
In France, one in five people will experience a depressive episode in their lifetime (Inserm). The Baromètre Santé 2017 indicates that approximately 10% of adults aged 18-75 experienced a depressive episode in the past 12 months. Depression can occur at any age, but it's most common between ages 15 and 44 (12-month prevalence of 11.2 to 11.4% in this age group).
The risk of recurrence is high: without treatment, 80% of people who experience a first episode will have another (Inserm). That's why appropriate treatment and follow-up are essential. The good news: in approximately 70% of cases, treatment is effective (Inserm). Depression is not a life sentence.
- Criteria: 5+ symptoms for 2+ weeks (DSM-5)
- Prevalence: 15-20% of the population in their lifetime (Inserm)
- Recurrence: 80% without treatment, but 70% effectiveness with treatment
- Mechanism: serotonin, dopamine, norepinephrine imbalance + impaired neuroplasticity
8 signs of depression
Click on a card to see real-life examples. If you recognize yourself in at least 5 of these signs for more than 2 weeks, with an intensity that weighs on your life, it's important to talk about it.
Persistent sadness
This isn't just a bad day. It's a deep sadness, present almost all day, almost every day. It doesn't always have a clear trigger. You might feel empty, hopeless, or have crying spells for no apparent reason.
Au quotidien
- • You wake up with a heaviness before the day even starts
- • You cry for no identifiable reason, or you feel unable to cry despite your suffering
- • Moments that used to make you happy now leave you completely indifferent
Loss of interest (anhedonia)
Anhedonia is one of the two cardinal symptoms of depression. It's the inability to feel pleasure in activities you used to enjoy. Sports, outings, hobbies, relationships — everything feels dull, meaningless.
Au quotidien
- • You no longer want to see your friends, even those you love
- • Your favorite hobby leaves you completely indifferent
- • You do things out of obligation, never out of desire
Fatigue and loss of energy
This isn't normal tiredness after a busy day. It's a deep exhaustion that doesn't go away with rest. Getting up in the morning, showering, preparing a meal — the simplest tasks become mountains. This fatigue is one of the most disabling symptoms.
Au quotidien
- • You sleep 10 hours and wake up just as tired as when you went to bed
- • Taking a shower or going grocery shopping requires superhuman effort
- • You regularly cancel plans because you don't have the energy
Sleep disturbances
Depression disrupts sleep in both directions. Either you suffer from insomnia (difficulty falling asleep, nighttime awakenings, early morning waking), or hypersomnia (sleeping excessively without ever feeling rested). Early morning waking, around 4-5am with an inability to fall back asleep, is particularly characteristic.
Au quotidien
- • You wake up at 4am with dark thoughts, unable to fall back asleep
- • You spend 12 hours in bed but never feel rested
- • You dread bedtime because your mind races
Appetite changes
Depression alters your relationship with food. Some people completely lose their appetite and lose weight without dieting. Others turn to food for comfort and gain weight. A weight change of more than 5% in one month without explanation is a warning sign.
Au quotidien
- • You forget to eat or food has lost its taste
- • You eat compulsively, especially in the evening, without being truly hungry
- • You've lost or gained several kilos without trying
Concentration difficulties
Depression affects cognitive functions. Concentration, memory, decision-making — everything becomes harder. You re-read the same page three times without retaining anything, you can't decide what to eat, you forget appointments. This brain fog is often confused with tiredness or lack of motivation.
Au quotidien
- • You can no longer follow a movie or read a book to the end
- • Making the simplest decision — even a trivial one — paralyzes you
- • At work, it takes you 3 times longer to do what used to be simple
Guilt and low self-worth
Depression distorts how you see yourself. You feel worthless, useless, guilty about everything — even things beyond your control. This self-deprecation is disproportionate and irrational, but it feels absolutely real when you're experiencing it. It's the depression talking, not reality.
Au quotidien
- • You feel guilty for being tired or for not feeling "okay"
- • You think you're a burden to your loved ones
- • You keep telling yourself you don't deserve help
Unexplained physical pain
Depression isn't just "in your head." It also manifests in the body: headaches, back pain, muscle tension, digestive issues. These somatic symptoms are often the first reason for a doctor's visit — and the underlying depression goes unnoticed. This is what's called masked depression.
Au quotidien
- • You have chronic back pain or headaches with no identified medical cause
- • You have persistent digestive problems (nausea, cramps, bloating)
- • You feel permanent muscle tension, especially in your neck and shoulders
Do you recognize yourself in these signs?
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Sadness, blues, or depression: the severity scale
It's normal to feel sad. Everyone goes through difficult times. But at what point does sadness become depression? This scale helps you situate yourself — without replacing professional advice. Anxiety is often associated with depression: if you also experience persistent anxiety, make note of it for your healthcare provider.
| Duration | Daily impact | What to do | |
|---|---|---|---|
| Passing sadness | A few hours to a few days | Mild — you continue to function normally | Normal reaction, no action needed |
| Feeling down | A few days to 2 weeks | Moderate — low mood, fewer desires | Rest, physical activity, talk to someone close |
| Mild depression (PHQ-9: 5-9) | 2 weeks or more | Noticeable difficulty — functioning takes effort | Self-assessment recommended, consult if it persists |
| Moderate depression (PHQ-9: 10-19) | 2 weeks or more | Significant — social and professional life affected | Consultation needed, psychotherapy recommended |
| Severe depression (PHQ-9: 20-27) | 2 weeks or more | Very intense — inability to function | Urgent consultation, combined treatment |
The PHQ-9 is a scientifically validated screening tool (Kroenke et al., 2001). It does not replace a clinical diagnosis. If you are in distress, call your local crisis helpline.
The different forms of depression
Seasonal depression (or seasonal affective disorder) occurs mainly in autumn-winter, when natural light decreases. It affects more women and people living in regions with low sunshine. The reference treatment is light therapy (daily exposure to a 10,000 lux lamp), often combined with psychotherapy.
Postpartum depression affects approximately 10% of women after childbirth (not to be confused with baby blues, which lasts 10 to 15 days and resolves on its own). It can appear in the weeks or months following birth and affects the mother-child bond. Early screening is essential. There's also melancholic depression, a severe form marked by profound psychomotor slowing, intense guilt, and high suicide risk — it requires urgent medical care. Finally, the line between burnout and depression is sometimes blurry: prolonged burnout can evolve into a major depressive episode.
The genetic component plays a role: having a parent who suffered from depression multiplies the risk by 2 to 4 (Inserm). But genes are not destiny — it's the gene-environment interactions that trigger or prevent the condition. Chronic stress, trauma, social isolation, or chronic illness are common triggers. In some people, depression is also associated with bipolar disorder — a differential diagnosis that only a professional can make.
- Seasonal: autumn-winter, treated with light therapy
- Postpartum: ~10% of women, early screening essential
- Genetic: 2-4x risk if a parent is affected, but not a certainty
5 myths about depression
Sadness is a normal, temporary emotion. Depression is a medical condition involving lasting neurobiological dysfunction. It goes beyond sadness: it includes loss of pleasure, fatigue, cognitive impairment, physical pain. And unlike sadness, it doesn't resolve on its own without treatment in most cases.
Antidepressants do not create addiction in the pharmacological sense. They don't cause tolerance or craving. However, abrupt discontinuation can cause withdrawal symptoms (dizziness, irritability, nausea), which is why stopping must be gradual and supervised by a doctor. Antidepressants generally take 2 to 4 weeks to show their full effect (Inserm).
Telling a depressed person to "snap out of it" is like asking a diabetic to produce insulin through willpower. Depression involves real neurobiological dysfunction: serotonin imbalance, impaired neuroplasticity, stress axis disruption. Willpower alone is not enough — and it's not the person's fault.
Anyone can develop depression. Risk factors are multiple: genetics, trauma, chronic stress, physical illness, isolation. Up to 40% of people with chronic disease (diabetes, cancer, fibromyalgia) develop depression (Inserm). "Strength of character" doesn't protect against a neurobiological disorder.
Treatment is effective in approximately 70% of cases (Inserm). One-third of patients achieve complete remission after 8 weeks of treatment, one-third significant improvement. Relapses do occur (80% without consolidation treatment), but appropriate follow-up — minimum 1 year after the first episode (Inserm) — significantly reduces this risk. Recovery is possible and common.
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Think you might have depression? Here's how to move forward
What you're feeling is real. You don't have to handle everything alone. Here are concrete steps, at your own pace.
Acknowledge what you're feeling
The first step is to accept that something isn't right — without judging yourself. Depression makes you believe it's your fault, that you're weak. That's not true. Acknowledging your suffering is already an act of courage.
Take a first self-assessment
Our self-assessment based on the PHQ-9 gives you a first look at your state in just a few minutes. It's free, confidential, and doesn't replace a diagnosis — but it helps you put words to what you're experiencing.
Talk to someone you trust
A friend, a family member, a colleague. You don't need to explain everything — just break the isolation. If you don't know who to turn to, crisis helplines are available 24/7, free, and confidential.
See a healthcare professional
Your general practitioner is often the first point of contact. They can assess your situation and refer you to a psychiatrist or psychologist. Treatment usually combines psychotherapy (CBT, interpersonal therapy) and, if needed, antidepressants.
Questions frequentes
Depression (major depressive episode) is a mood disorder recognized by the WHO and DSM-5. It's characterized by at least 5 symptoms present daily for at least 2 weeks: persistent sadness, loss of interest, fatigue, sleep disturbances, appetite changes, concentration difficulties, guilt, and sometimes suicidal thoughts. It affects 15 to 20% of the population over a lifetime (Inserm).
Feeling down is a temporary state of low mood, often linked to an identifiable event (breakup, failure, fatigue). It lasts a few days to 2 weeks and resolves on its own. Depression is a medical condition: symptoms persist beyond 2 weeks, are more intense, and impact daily functioning. It's the duration, intensity, and impact that make the difference — not the trigger.
Ask yourself: for more than 2 weeks, have I been feeling sad almost every day? Have I lost interest in things I used to enjoy? Are my energy, sleep, or appetite disrupted? If you answer yes to several of these, a self-assessment using the PHQ-9 can help clarify things. But only a healthcare professional can make a diagnosis.
Yes. Treatment is effective in approximately 70% of cases (Inserm). It usually combines psychotherapy (cognitive-behavioral or interpersonal therapy) and, if needed, antidepressants (mainly SSRIs). Antidepressants take 2 to 4 weeks to reach full effect. Treatment for a first episode should last at least 1 year to reduce relapse risk. For severe resistant cases, electroconvulsive therapy (ECT) is effective in 90 to 95% of cases (Inserm).
Our self-assessment on Deep Tests is based on the PHQ-9, a scientifically validated tool (Kroenke, Spitzer & Williams, 2001). It's free, confidential, and gives you an instant result with a severity score. Note: it's a screening and self-assessment tool, not a medical diagnosis. If your score indicates signs of depression, see a professional.
Seek help immediately if you have suicidal thoughts, if you're harming yourself, or if you feel you might act on it. Call your local crisis helpline (available 24/7, free, and confidential). Depression multiplies suicide risk by 30 during episodes (Inserm). Asking for help is not a sign of weakness — it's an act of survival.
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Avertissement
This guide is for informational purposes only. It does not replace a medical diagnosis. If you are in distress, talk to a healthcare professional. You can also contact your local crisis helpline (available 24/7, free, and confidential).
Sources
- Inserm — Depression: understanding it better to treat it durably (information dossier)
- HAS — Major depressive episode in adults: primary care management
- WHO — Depression (fact sheet, 2023)
- DSM-5 — Diagnostic Criteria for Major Depressive Episode (APA, 2013)
- Kroenke, Spitzer & Williams — The PHQ-9: Validity of a Brief Depression Severity Measure (J Gen Intern Med, 2001)