Suicidal behavior is a major public health issue and there are currently no specific treatments for it.

However, lithium, the reference treatment for bipolar disorder, have been shown to be effective in preventing suicidal risk.

Apart from drug treatments, lithium is present in our environment and its levels varies from one individual to another, depending, especially, on diet.

Knowing that patients with a mood disorder generally have a poor lifestyle and a less rich and varied diet than the general population, variations in basal lithium levels can be expected in these patients.

This study aims to assess the rate of depressed patients (unipolar or bipolar) with basal plasma lithium levels above 0.1 µeq/L.

It also aims to :

• compare basal plasma lithium levels according to the occurrence of a suicidal event in the year prior to inclusion ;
• assess the association of lithium levels with the intensity of current suicidal ideation ;
• assess the association of lithium levels with impulsiveness ;
• assess the association of lithium levels with characteristics of bipolar disorder (for patients with bipolar disorder) ;
• assess the association of lithium levels with emotional lability ;
• assess, in the patients with a suicidal event in the year prior to the inclusion, the association of lithium levels with the characteristics of suicide attempts

To do so, 158 patients currently suffering from a major depressive disorder and who have not received any lithium treatment over the last year, will be included and divided in two groups :

1. Depressed patients with a history of suicidal event over the last 12 months (suicide attempters/ideations) ;
2. Depressed patients with no history of suicidal event over the last 12 months (affective controls).

Following a clinical assessment, a blood sample will be collected from each participant to measure basal plasma lithium levels.

Study participation will be done in one day.

The investigators expect :

1. an inverse association between lithium levels and suicidal events in patients
2. an inverse association between lithium levels and impulsiveness and aggression in patients This study will contribute to a better knowledge on suicidal behavior, especially by confirming the protective effect of lithium and improving the understanding of the mechanisms involved.

This knowledge will eventually make it possible to develop prevention and management strategies.

More appropriate prevention and management strategies better adapted to patients at risk of suicide.

Inclusion Criteria:

• 18 years old or over
• Current major depressive episode according to the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders) criteria
• No lithium-based treatment over the last 12 months
• For suicide attempters/ideations only : suicidal event over the last 12 months
• For affective controls only : no suicidal event over the last 12 months

Exclusion Criteria:

• Lifetime diagnosis of schizoaffective disorder, schizophrenia or psychosis
• Pregnancy or breastfeeding
• Deprivation of freedom (by judicial or administrative decision)
• Legal protection measure (guardianship or curators)
• Inability to understand experimental procedures
• No affiliation to the French National Social Security System
• No consent to participate in the study

Patients currently suffering from a major depressive disorder, with ot without a history of suicidal event over the last 12 months, seen in consultation or hospitalization in the Psychiatric Emergencies and Post Acute Care of Montpellier Univeristy Hospital.