Substance abuse is the second most common risk factor for suicide after major depression and bipolar disorder. Both chronic substance misuse as well as acute intoxication are associated. When combined with personal grief, such as bereavement, the risk is further increased. Substance misuse is also associated with mental health disorders.

Most people are under the influence of sedative-hypnotic drugs (such as alcohol or benzodiazepines) when they die by suicide with alcoholism present in between 15% and 61% of cases. Use of prescribed benzodiazepines is asscociated with an increased rate of attempted and completed suicide. The prosuicidal effects of benzodiazepines are suspected to be due to a psychiatric disturbance caused by side effects or withdrawal symptoms. Countries that have higher rates of alcohol use and a greater density of bars generally also have higher rates of suicide. About 2.2–3.4% of those who have been treated for alcoholism at some point in their life die by suicide. Alcoholics who attempt suicide are usually male, older, and have tried to take their own lives in the past. Between 3 and 35% of deaths among those who use heroin are due to suicide (approximately fourteenfold greater than those who do not use). In adolescents who misuse alcohol, neurological and psychological dysfunctions may contribute to the increased risk of suicide.

The misuse of cocaine and methamphetamine has a high correlation with suicide. In those who use cocaine the risk is greatest during the withdrawal phase. Those who used inhalants are also at significant risk with around 20% attempting suicide at some point and more than 65% considering it. Smoking cigarettes is associated with risk of suicide. There is little evidence as to why this association exists; however it has been hypothesized that those who are predisposed to smoking are also predisposed to suicide, that smoking causes health problems which subsequently make people want to end their life, and that smoking affects brain chemistry causing a propensity for suicide. Cannabis however does not appear to independently increase the risk.

Problem gambling is associated with increased suicidal ideation and attempts compared to the general population. Between 12 and 24% pathological gamblers attempt suicide. The rate of suicide among their spouses is three times greater than that of the general population. Other factors that increase the risk in problem gamblers include mental illness, alcohol and drug misuse.

Research has found that drinking reduces the risk of developing gallstones. Compared with alcohol abstainers, the relative risk of gallstone disease, controlling for age, sex, education, smoking, and body mass index, is 0.83 for occasional and regular moderate drinkers (< 25 ml of ethanol per day), 0.67 for intermediate drinkers (25-50 ml per day), and 0.58 for heavy drinkers. This inverse association was consistent across strata of age, sex, and body mass index." Frequency of drinking also appears to be a factor. "An increase in frequency of alcohol consumption also was related to decreased risk. Combining the reports of quantity and frequency of alcohol intake, a consumption pattern that reflected frequent intake (5-7 days/week) of any given amount of alcohol was associated with a decreased risk, as compared with nondrinkers. In contrast, infrequent alcohol intake (1-2 days/week) showed no significant association with risk."

A large self-reported study published in 1998 found no correlation between gallbladder disease and multiple factors including smoking, alcohol consumption, hypertension, and coffee consumption. A retrospective study from 1997 found vitamin C (ascorbic acid) supplement use in drinkers was associated with a lower prevalence of gallbladder disease, but this association was not seen in non-drinkers.

The impact of alcohol on weight-gain is contentious: some studies find no effect, others find decreased or increased effect on weight gain.

Alcohol use increases the risk of chronic gastritis (stomach inflammation); it is one cause of cirrhosis, hepatitis, and pancreatitis in both its chronic and acute forms.

Substance misuse, dependence and withdrawal are associated with self-harm. Benzodiazepine dependence as well as benzodiazepine withdrawal is associated with self-harming behaviour in young people. Alcohol is a major risk factor for self-harm. A study which analysed self-harm presentations to emergency rooms in Northern Ireland found that alcohol was a major contributing factor and involved in 63.8% of self-harm presentations. A recent study in the relation between cannabis use and deliberate self-harm (DSH) in Norway and England found that, in general, cannabis use may not be a specific risk factor for DSH in young adolescents.

Alcohol abuse is said to be most common in people aged between 15 and 24 years, according to Moreira 2009. However, this particular study of 7275 college students in England collected no comparative data from other age groups or countries.

Causes of alcohol abuse are complex and are likely the combination of many factors, from coping with stress to childhood development. The US Department of Health & Human Services identifies several factors influencing adolescent alcohol use, such as risk-taking, expectancies, sensitivity and tolerance, personality and psychiatric comorbidity, hereditary factors, and environmental aspects. Studies show that child maltreatment such as neglect, physical, and/or sexual abuse, as well as having parents with alcohol abuse problems, increases the likelihood of that child developing alcohol use disorders later in life. According to Shin, Edwards, Heeren, & Amodeo (2009), underage drinking is more prevalent among teens that experienced multiple types of childhood maltreatment regardless of parental alcohol abuse, putting them at a greater risk for alcohol use disorders. Genetic and environmental factors play a role in the development of alcohol use disorders, depending on age. The influence of genetic risk factors in developing alcohol use disorders increase with age ranging from 28% in adolescence and 58% in adults.

In order to maintain high-quality performance, some musicians take chemical substances. Some musicians take drugs or alcohol to deal with the stress of performing. As a group they have a higher rate of substance abuse. The most common chemical substance which is abused by pop musicians is cocaine, because of its neurological effects. Stimulants like cocaine increase alertness and cause feelings of euphoria, and can therefore make the performer feel as though they in some ways ‘own the stage’. One way in which substance abuse is harmful for a performer (musicians especially) is if the substance being abused is aspirated. The lungs are an important organ used by singers, and addiction to cigarettes may seriously harm the quality of their performance. Smoking causes harm to alveoli, which are responsible for absorbing oxygen.

Abuse during childhood is accepted as a primary social factor increasing the incidence of self-harm, as is bereavement, and troubled parental or partner relationships. Factors such as war, poverty, and unemployment may also contribute. Self-harm is frequently described as an experience of depersonalisation or a dissociative state. As many as 70% of individuals with borderline personality disorder engage in self-harm. An estimated 30% of individuals with autism spectrum disorders engage in self-harm at some point, including eye-poking, skin-picking, hand-biting, and head-banging.

Street children in many developing countries are a high risk group for substance misuse, in particular solvent abuse. Drawing on research in Kenya, Cottrell-Boyce argues that "drug use amongst street children is primarily functional – dulling the senses against the hardships of life on the street – but can also provide a link to the support structure of the ‘street family’ peer group as a potent symbol of shared experience."

The cause of alcohol abuse is complex. Alcohol abuse is related to economic and biological origins and is associated with adverse health consequences. Peer pressure influences individuals to abuse alcohol; however, most of the influence of peers is due to inaccurate perceptions of the risks of alcohol abuse. According to Gelder, Mayou and Geddes (2005) easy accessibility of alcohol is one of the reasons people engage in alcohol abuse as this substance is easily obtained in shops. Another influencing factor among adolescents and college students are the perceptions of social norms for drinking; people will often drink more to keep up with their peers, as they believe their peers drink more than they actually do. They might also expect to drink more given the context (e.g. sporting event, fraternity party, etc.). This perception of norms results in higher alcohol consumption than is normal.

Alcohol abuse is also associated with acculturation, because social and cultural factors such as an ethnic group’s norms and attitudes can influence alcohol abuse.

Promoters of this suicide method recommend it to terminally ill patients. However, across the world, most people who use suicide bags are physically healthy. Instead of having incurable cancer or other life-threatening physical diseases, most of the users have psychiatric disorders or substance abuse problems that might possibly be addressed through medical and psychological treatment. The demographics of its users varies; in one survey, the method had been used mostly by middle-aged adults in failing health, who were attracted to the relative nonviolence of the method.

This suicide method is also typically used by younger or middle-aged adults, rather than by older adults. In the US, it is more commonly chosen by non-Hispanic white males than by women or people of other races.

Like their adult counterparts, children and adolescent depression sufferers are at an increased risk of attempting or committing suicide. Suicide is the third leading cause of death among 15-19 year olds. Adolescent males may be at an even higher risk of suicidal behavior if they also present with a conduct disorder. In the 1990s, the National Institute of Mental Health (NIMH) found that up to 7% of adolescents who develop major depressive disorder may commit suicide as young adults. Such statistics demonstrate the importance of interventions by family and friends, as well as the importance of early diagnosis and treatment by medical staff, to prevent suicide among depressed or at-risk youth.

In childhood, boys and girls appear to be at equal risk for depressive disorders; during adolescence, however, girls are twice as likely as boys to develop depression. Before adolescence rates of depression are about the same in girls and boys, it is not until between the ages of 11-13 that is begins to change.Young girls around this age, physically, go through more changes than young boys which put that a higher risk for depression and hormonal imbalance. The gender gap in depression between adolescent men and women is mostly due to young women's lower levels of positive thinking, need for approval, and self-focusing negative conditions. Frequent exposure to victimization or bullying was related to high risks of depression, ideation and suicide attempts compare to those not involved in bullying. Nicotine dependence is also associated with depression, anxiety, and poor dieting, mostly in young men. Although causal direction has not been established, involvement in any sex or drug use is cause for concern. Children who develop major depression are more likely to have a family history of the disorder (often a parent who experienced depression at an early age) than patients with adolescent- or adult-onset depression. Adolescents with depression are also likely to have a family history of depression, though the correlation is not as high as it is for children.

Russel Ogden (2002) said that the existence of "how-to" literature involving the suicide bag has been "shown to influence the choice of suicide method but not the overall suicide rate, and that an emerging counterculture of death providers, operating outside of the traditional medicolegal framework of health care, was placing assisted death outside the normative gaze of medicine". In 2010, Ogden and colleagues observed four cases of assisted suicide with helium delivered by face mask. The authors stated that a hood method might be able to play a role in "demedicalising assisted suicide". Ogden views a bag and inert gas as "the quickest way to go; used properly, you're unconscious after the second breath and dead in about 10 minutes".

Clinical psychologist Phillip Kleespies said that Ogden's work calls attention to some of the risks associated with covert assisted suicide using unregulated methods like the suicide bag with inert gas. Disagreeing with Ogden and other right-to-die proponents, who call the method "swift, highly lethal and painless", Kleespies feels it is an undignified, impersonal and "hurried" manner of death.

A study poses the dilemma for medical ethicists and the general public who "may also want to carefully weigh the unintended adverse consequences of widely disseminated suicide methods likely to appeal to some depressed persons (irrespective of their physical health status or age) against the putative benefits associated with making these methods more widely known and available".

The cause of major depressive disorder is unknown. The biopsychosocial model proposes that biological, psychological, and social factors all play a role in causing depression. The diathesis–stress model specifies that depression results when a preexisting vulnerability, or diathesis, is activated by stressful life events. The preexisting vulnerability can be either genetic, implying an interaction between nature and nurture, or schematic, resulting from views of the world learned in childhood.

Childhood abuse, either physical, sexual or psychological are all risk factors for depression, among other psychiatric issues that co-occur such as anxiety and drug abuse. Childhood trauma also correlates with severity of depression, lack of response to treatment and length of illness. However, some are more susceptible to developing mental illness such as depression after trauma, and various genes have been suggested to control susceptibility.

Major depressive episodes often resolve over time whether or not they are treated. Outpatients on a waiting list show a 10–15% reduction in symptoms within a few months, with approximately 20% no longer meeting the full criteria for a depressive disorder. The median duration of an episode has been estimated to be 23 weeks, with the highest rate of recovery in the first three months.

Studies have shown that 80% of those suffering from their first major depressive episode will suffer from at least 1 more during their life, with a lifetime average of 4 episodes. Other general population studies indicate that around half those who have an episode recover (whether treated or not) and remain well, while the other half will have at least one more, and around 15% of those experience chronic recurrence. Studies recruiting from selective inpatient sources suggest lower recovery and higher chronicity, while studies of mostly outpatients show that nearly all recover, with a median episode duration of 11 months. Around 90% of those with severe or psychotic depression, most of whom also meet criteria for other mental disorders, experience recurrence.

Recurrence is more likely if symptoms have not fully resolved with treatment. Current guidelines recommend continuing antidepressants for four to six months after remission to prevent relapse. Evidence from many randomized controlled trials indicates continuing antidepressant medications after recovery can reduce the chance of relapse by 70% (41% on placebo vs. 18% on antidepressant). The preventive effect probably lasts for at least the first 36 months of use.

Those people experiencing repeated episodes of depression require ongoing treatment in order to prevent more severe, long-term depression. In some cases, people must take medications for long periods of time or for the rest of their lives.

Cases when outcome is poor are associated with inappropriate treatment, severe initial symptoms that may include psychosis, early age of onset, more previous episodes, incomplete recovery after 1 year, pre-existing severe mental or medical disorder, and family dysfunction as well.

Depressed individuals have a shorter life expectancy than those without depression, in part because depressed patients are at risk of dying by suicide. However, they also have a higher rate of dying from other causes, being more susceptible to medical conditions such as heart disease. Up to 60% of people who die by suicide have a mood disorder such as major depression, and the risk is especially high if a person has a marked sense of hopelessness or has both depression and borderline personality disorder. The lifetime risk of suicide associated with a diagnosis of major depression in the US is estimated at 3.4%, which averages two highly disparate figures of almost 7% for men and 1% for women (although suicide attempts are more frequent in women). The estimate is substantially lower than a previously accepted figure of 15%, which had been derived from older studies of hospitalized patients.

Depression is often associated with unemployment and poverty. Major depression is currently the leading cause of disease burden in North America and other high-income countries, and the fourth-leading cause worldwide. In the year 2030, it is predicted to be the second-leading cause of disease burden worldwide after HIV, according to the World Health Organization. Delay or failure in seeking treatment after relapse, and the failure of health professionals to provide treatment, are two barriers to reducing disability.

Several studies have shown that the risk of suicide is higher in patients who suffer from Bipolar II than those who suffer from Bipolar I, and especially higher than patients who suffer from major depressive disorder.

In results of a summary of several lifetime study experiments, it was found that 24% of Bipolar II patients experienced suicidal ideation or suicide attempts compared to 17% in Bipolar I patients and 12% in major depressive patients. Bipolar disorders, in general, are the third leading cause of death in 15- to 24-year-olds. Bipolar II patients were also found to employ more lethal means and have more complete suicides overall.

Bipolar II patients have several risk factors that increase their risk of suicide. The illness is very recurrent and results in severe disabilities, interpersonal relationship problems, barriers to academic, financial, and vocational goals, and a loss of social standing in their community, all of which increase the likelihood of suicide. Mixed symptoms and rapid-cycling, both very common in Bipolar II, are also associated with an increased risk of suicide. The tendency for Bipolar II to be misdiagnosed and treated ineffectively, or not at all in some cases, leads to an increased risk.

As a result of the high suicide risk for this group, reducing the risk and preventing attempts remains a main part of the treatment; a combination of self-monitoring, close supervision by a therapist, and faithful adherence to their medication regimen will help to reduce the risk and prevent the likelihood of a completed suicide.

Comorbid conditions are extremely common in individuals with BP-II. In fact, individuals are twice as likely to present a comorbid disorder than not. These include anxiety, eating, personality (cluster B), and substance use disorders. For bipolar II disorder, the most conservative estimate of lifetime prevalence of alcohol or other drug abuse disorders is 20%. In patients with comorbid substance abuse disorder and BP-II, episodes have a longer duration and treatment compliance decreases. Preliminary studies suggest that comorbid substance abuse is also linked to increased risk of suicidality.

Estimates of the numbers of people suffering from major depressive episodes and Major Depressive Disorder (MDD) vary significantly. In their lifetime, 10% to 25% of women, and 5% to 12% of men will suffer a major depressive episode. Fewer people, between 5% and 9% of women and between 2% and 3% of men, will have MDD, or full-blown depression. The greatest differences in numbers of men and women diagnosed are found in the United States and Europe. The peak period of development is between the ages of 25 and 44 years. Onset of major depressive episodes or MDD often occurs to people in their mid-20s, and less often to those over 65. Prepubescent girls and boys are affected equally. The symptoms of depression are the same in both children and adolescents though there is evidence that their expression within an individual may change as he or she ages.

In a National Institute of Mental Health study, researchers found that more than 40 percent of people with post-traumatic stress disorder suffered from depression 4 months after the traumatic event they experienced.

Cultural factors can influence the symptoms displayed by a person experiencing a major depressive episode. The values of a specific culture may also influence which symptoms are more concerning to the person or and their friends and family. It is essential that a trained professional knows not to dismiss specific symptoms as merely being the "norm" of a culture.

Women who have recently given birth may be at increased risk for having a major depressive episode. This is referred to as postpartum depression and is a different health condition than the baby blues, a low mood that resolves within 10 days after delivery.

While the causes of PPD are not understood, a number of factors have been suggested to increase the risk:

- Prenatal depression or anxiety

- A personal or family history of depression

- Moderate to severe premenstrual symptoms

- Maternity blues

- Birth-related psychological trauma

- Birth-related physical trauma

- Previous stillbirth or miscarriage

- Formula-feeding rather than breast-feeding

- Cigarette smoking

- Low self-esteem

- Childcare or life stress

- Low social support

- Poor marital relationship or single marital status

- Low socioeconomic status

- Infant temperament problems/colic

- Unplanned/unwanted pregnancy

- Elevated prolactin levels

- Oxytocin depletion

Of these risk factors, formula-feeding, a history of depression, and cigarette smoking have been shown to have additive effects.

These above factors are known to correlate with PPD. This correlation does not mean these factors are causal. Rather, they might both be caused by some third factor. Contrastingly, some factors almost certainly attribute to the cause of postpartum depression, such as lack of social support.

Not surprisingly, women with fewer resources indicate a higher level of postpartum depression and stress than those women with more resources, such as financial. Rates of PPD have been shown to decrease as income increases. Women with fewer resources may be more likely to have an unintended or unwanted pregnancy, increasing risk of PPD. Women with fewer resources may also include single mothers of low income. Single mothers of low income may have more limited access to resources while transitioning into motherhood.

Studies have also shown a correlation between a mother's race and postpartum depression. African American mothers have been shown to have the highest risk of PPD at 25%, while Asian mothers had the lowest at 11.5%, after controlling for social factors such as age, income, education, marital status, and baby's health. The PPD rates for First Nations, Caucasian and Hispanic women fell in between.

Sexual orientation has also been studied as a risk factor for PPD. In a 2007 study conducted by Ross and colleagues, lesbian and bisexual mothers were tested for PPD and then compared with a heterosexual sample group. It was found that lesbian and bisexual biological mothers had significantly higher Edinburgh Postnatal Depression Scale scores than did the heterosexual women in the sample. These higher rates of PPD in lesbian/bisexual mothers may reflect less social support, particularly from their families of origin and additional stress due to homophobic discrimination in society.

A correlation between postpartum thyroiditis and postpartum depression has been proposed but remains controversial. There may also be a link between postpartum depression and anti-thyroid antibodies.

Major Depression is a mental disorder characterized by an all-encompassing low mood accompanied by low self-esteem, and loss of interest or pleasure in normally enjoyable activities.Nearly 5 million of the 31 million Americans who are 65 years or older are clinically depressed, and 1 million have major depression. Approximately 3 percent of healthy elderly persons living in the community have major depression. Recurrence may be as high as 40 percent. Suicide rates are nearly twice as high in depressed patients as in the general population. Major depression is more common in medically ill patients who are older than 70 years and hospitalized or institutionalized. Severe or chronic diseases associated with high rates of depression include stroke (30 to 60 percent), coronary heart disease (8 to 44 percent), cancer (1 to 40 percent), Parkinson's disease (40 percent), Alzheimer's disease (20 to 40 percent), and dementia (17 to 31 percent).

Minor depression is a clinically significant depressive disorder that does not fulfill the duration criterion or the number of symptoms necessary for the diagnosis of major depression. Minor depression, which is more common than major depression in elderly patients, may follow a major depressive episode. It also can be a reaction to routine stressors in older populations. Fifteen to 50 percent of patients with minor depression develop major depression within two years.

Various factors have been found to be more associated with a diagnosis of AD than other axis I disorders, including:

- younger age

- more identified psychosocial and environmental problems

- increased suicidal behaviour, more likely to be rated as improved by the time of discharge from mental healthcare

- less frequent previous psychiatric history

- shorter length of treatment

Those exposed to repeated trauma are at greater risk, even if that trauma is in the distant past. Age can be a factor due to young children having fewer coping resources; children are also less likely to assess the consequences of a potential stressor.

A stressor is generally an event of a serious, unusual nature that an individual or group of individuals experience. The stressors that cause adjustment disorders may be grossly traumatic or relatively minor, like loss of a girlfriend/boyfriend, a poor report card, or moving to a new neighborhood. It is thought that the more chronic or recurrent the stressor, the more likely it is to produce a disorder. The objective nature of the stressor is of secondary importance. Stressors' most crucial link to their pathogenic potential is their perception by the patient as stressful. The presence of a causal stressor is essential before a diagnosis of adjustment disorder can be made.

There are certain stressors that are more common in different age groups:

Adulthood:

- Marital conflict

- Financial conflict

- Health issues with Oneself/Partner or Dependent children

- Personal tragedy (Death/personal loss)

- Loss of job or unstable employment conditions (e.g. Corporate takeover/redundancy)

Adolescence and childhood:

- Family conflict/parental separation

- School problems/changing schools

- Sexuality issues

- Death/illness/trauma in the family

In a study conducted from 1990 to 1994 on 89 psychiatric outpatient adolescents, 25% had attempted suicide in which 37.5% had misused alcohol, 87.5% displayed aggressive behaviour, 12.5% had learning difficulties, and 87.5% had anxiety symptoms.

Postpartum depression is found across the globe, with rates varying from 11% to 42%. Around 3% to 6% of women will experience depression during pregnancy or shortly after giving birth. About 1 in 750 mothers will have postpartum depression with psychosis and their risk is higher if they have had postpartum episodes in the past.

Major depressive episodes may show comorbidity (association) with other physical and mental health problems. About 20-25% of individuals with a chronic general medical condition will develop major depression. Common comorbid disorders include: eating disorders, substance-related disorders, panic disorder, and obsessive-compulsive disorder. Up to 25% of people who experience a major depressive episode have a pre-existing dysthymic disorder.

Some persons who have a fatal illness or are at the end of their life may experience depression, although this is not universal.

According to a substantial amount of epidemiology studies conducted, women are twice as likely to develop certain mood disorders, such as major depression. Although there is an equal number of men and women diagnosed with bipolar II disorder, women have a slightly higher frequency of the disorder.

In 2011, mood disorders were the most common reason for hospitalization among children aged 1–17 years in the United States, with approximately 112,000 stays. Mood disorders were top principal diagnosis for Medicaid super-utilizers in the United States in 2012. Further, a study of 18 States found that mood disorders accounted for the highest number of hospital readmissions among Medicaid patients and the uninsured, with 41,600 Medicaid patients and 12,200 uninsured patients being readmitted within 30 days of their index stay—a readmission rate of 19.8 per 100 admissions and 12.7 per 100 admissions, respectively. In 2012, mood and other behavioral health disorders were the most common diagnoses for Medicaid-covered and uninsured hospital stays in the United States (6.1% of Medicaid stays and 5.2% of uninsured stays).

A study conducted in 1988 to 1994 amongst young American adults involved a selection of demographic and health characteristics. A population-based sample of 8,602 men and women ages 17–39 years participated. Lifetime prevalence were estimated based on six mood measures:

1. major depressive episode (MDE) 8.6%,

2. major depressive disorder with severity (MDE-s) 7.7%,

3. dysthymia 6.2%,

4. MDE-s with dysthymia 3.4%,

5. any bipolar disorder 1.6%, and

6. any mood disorder 11.5%.