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.

Bipolar disorder can cause suicidal ideation that leads to suicidal attempts. Individuals whose bipolar disorder begins with a depressive or mixed affective episode seem to have a poorer prognosis and an increased risk of suicide. One out of two people with bipolar disorder attempt suicide at least once during their lifetime and many attempts are successfully completed. The annual average suicide rate is 0.4 percent, which is 10–20 times that of the general population. The standardized mortality ratio from suicide in bipolar disorder is between 18 and 25. The lifetime risk of suicide has been estimated to be as high as 20 percent in those with bipolar disorder.

Depressed mood can be the result of a number of infectious diseases, nutritional deficiencies, neurological conditions and physiological problems, including hypoandrogenism (in men), Addison's disease, Cushing's syndrome, hypothyroidism, Lyme disease, multiple sclerosis, Parkinson's disease, chronic pain, stroke, diabetes, and cancer.

Approximately three percent of people who are suffering from alcoholism experience psychosis during acute intoxication or withdrawal. Alcohol related psychosis may manifest itself through a kindling mechanism. The mechanism of alcohol-related psychosis is due to the long-term effects of alcohol resulting in distortions to neuronal membranes, gene expression, as well as thiamin deficiency. It is possible in some cases that alcohol abuse via a kindling mechanism can cause the development of a chronic substance induced psychotic disorder, i.e. schizophrenia. The effects of an alcohol-related psychosis include an increased risk of depression and suicide as well as causing psychosocial impairments.

According to some studies, the more often cannabis is used the more likely a person is to develop a psychotic illness, with frequent use being correlated with twice the risk of psychosis and schizophrenia. While cannabis use is accepted as a contributory cause of schizophrenia by some, it remains controversial, with pre-existing vulnerability to psychosis emerging as the key factor that influences the link between cannabis use and psychosis. Some studies indicate that the effects of two active compounds in cannabis, tetrahydrocannabinol (THC) and cannabidiol (CBD), have opposite effects with respect to psychosis. While THC can induce psychotic symptoms in healthy individuals, CBD may reduce the symptoms caused by cannabis.

Cannabis use has increased dramatically over the past few decades whereas the rate of psychosis has not increased. Together, these findings suggest that cannabis use may hasten the onset of psychosis in those who may already be predisposed to psychosis. High-potency cannabis use indeed seems to accelerate the onset of psychosis in predisposed patients. A 2012 study concluded that cannabis plays an important role in the development of psychosis in vulnerable individuals, and that cannabis use in early adolescence should be discouraged.

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.

A lifelong condition with periods of partial or full recovery in between recurrent episodes of relapse, bipolar disorder is considered to be a major health problem worldwide because of the increased rates of disability and premature mortality. It is also associated with co-occurring psychiatric and medical problems and high rates of initial under- or misdiagnosis, causing a delay in appropriate treatment interventions and contributing to poorer prognoses. After a diagnosis is made, it remains difficult to achieve complete remission of all symptoms with the currently available psychiatric medications and symptoms often become progressively more severe over time.

Compliance with medications is one of the most significant factors that can decrease the rate and severity of relapse and have a positive impact on overall prognosis. However, the types of medications used in treating BD commonly cause side effects and more than 75% of individuals with BD inconsistently take their medications for various reasons.

Of the various types of the disorder, rapid cycling (four or more episodes in one year) is associated with the worst prognosis due to higher rates of self-harm and suicide. Individuals diagnosed with bipolar who have a family history of bipolar disorder are at a greater risk for more frequent manic/hypomanic episodes. Early onset and psychotic features are also associated with worse outcomes, as well as subtypes that are nonresponsive to lithium.

Early recognition and intervention also improve prognosis as the symptoms in earlier stages are less severe and more responsive to treatment. Onset after adolescence is connected to better prognoses for both genders, and being male is a protective factor against higher levels of depression. For women, better social functioning prior to developing bipolar disorder and being a parent are protective towards suicide attempts.

Studies have shown that those who fall into minorities due to either their gender identity or sexual orientation (such as those that identify as LGBT), are more prone to depression.

Depression is especially common among those over 65 years of age and increases in frequency with age beyond this age. In addition the risk of depression increases in relation to the age and frailty of the individual. Depression is one the most important factors which negatively impact quality of life in adults as well as the elderly. Both symptoms and treatment among the elderly differ from those of the rest of the adult populations.

As with many other diseases it is common among the elderly not to present classical depressive symptoms. Diagnosis and treatment is further complicated in that the elderly are often simultaneously treated with a number of other drugs, and often have other concurrent diseases. Treatment differs in that studies of SSRI-drugs have shown lesser and often inadequate effect among the elderly, while other drugs with more clear effects have adverse effects which can be especially difficult to handle among the elderly. Duloxetine is an SNRI-drug with documented effect on recurring depression among the elderly, but has adverse effects in form of dizziness, dryness of the mouth, diarrhea, and constipation.

Problem solving therapy was as of 2015 the only psychological therapy with proven effect, and can be likened to a simpler form of cognitive behavioral therapy. However, elderly with depression are seldom offered any psychological treatment, and the evidence surrounding which other treatments are effective is incomplete. Electroconvulsive therapy (ECT or electric-shock therapy) has been used as treatment of the elderly, and register-studies suggest it is effective although less so among the elderly than among the rest of the adult population.

The risks involved with treatment of depression among the elderly as opposed to benefits is not entirely clear. Awaiting more evidence on how depression-treatment among the elderly is best designed it is important to follow up treatment results, and to reconsider changing treatments if it does not help.

Trials are looking at the effects of botulinum toxins on depression. The idea is that the drug is used to make the person look less frowning and that this stops the negative facial feedback from the face. In 2015 it turned out, however, that the partly positive effects that had been observed until then could have been placebo effects.

MDD has been studied by taking MRI scans of patients with depression have revealed a number of differences in brain structure compared to those who are not depressed. Meta-analyses of neuroimaging studies in major depression reported that, compared to controls, depressed patients had increased volume of the lateral ventricles and adrenal gland and smaller volumes of the basal ganglia, thalamus, hippocampus, and frontal lobe (including the orbitofrontal cortex and gyrus rectus). Hyperintensities have been associated with patients with a late age of onset, and have led to the development of the theory of vascular depression.

A previous history of suicide attempts is the most accurate predictor of completed suicide. Approximately 20% of suicides have had a previous attempt, and of those who have attempted suicide, 1% complete suicide within a year and more than 5% die by suicide within 10 years. Acts of self-harm are not usually suicide attempts and most who self-harm are not at high risk of suicide. Some who self-harm, however, do still end their life by suicide, and risk for self-harm and suicide may overlap.

Premorbidity refers to the state of functionality prior to the onset of a disease or illness. It is most often used in relation to psychological function (e.g. premorbid personality or premorbid intelligence), but can also be used in relation to other medical conditions (e.g. premorbid lung function or premorbid heart rate).

Another theory is that there may be shared risk factors that can lead to both substance abuse and mental illness. Mueser hypothesizes that these may include factors such as social isolation, poverty, lack of structured daily activity, lack of adult role responsibility, living in areas with high drug availability, and association with people who already misuse drugs.

Other evidence suggests that traumatic life events, such as sexual abuse, are associated with the development of psychiatric problems and substance abuse.

According to research by RM Carney et al., any history of child depression influences the occurrence of adolescent cardiac risk factors, even if individuals no longer suffer from depression. They are much more likely to develop heart disease as adults.

Risk factors for mental illness include genetic inheritance, such as parents having depression, or a propensity for high neuroticism or "emotional instability".

In depression, parenting risk factors include parental unequal treatment, and there is association with high cannabis use.

In schizophrenia and psychosis, risk factors include migration and discrimination, childhood trauma, bereavement or separation in families, and abuse of drugs, including cannabis, and urbanicity.

In anxiety, risk factors may include family history (e.g. of anxiety), temperament and attitudes (e.g. pessimism), and parenting factors including parental rejection, lack of parental warmth, high hostility, harsh discipline, high maternal negative affect, anxious childrearing, modelling of dysfunctional and drug-abusing behaviour, and child abuse (emotional, physical and sexual).

Environmental events surrounding pregnancy and birth have also been implicated. Traumatic brain injury may increase the risk of developing certain mental disorders. There have been some tentative inconsistent links found to certain viral infections, to substance misuse, and to general physical health.

Social influences have been found to be important, including abuse, neglect, bullying, social stress, traumatic events and other negative or overwhelming life experiences. For bipolar disorder, stress (such as childhood adversity) is not a specific cause, but does place genetically and biologically vulnerable individuals at risk for a more severe course of illness. The specific risks and pathways to particular disorders are less clear, however. Aspects of the wider community have also been implicated, including employment problems, socioeconomic inequality, lack of social cohesion, problems linked to migration, and features of particular societies and cultures.

According to research conducted by Laura P. Richardson et al., major depression occurred in 7% of the cohort during early adolescence (11, 13, and 15 years of age) and 27% during late adolescence (18 and 21 years of age). At 26 years of age, 12% of study members were obese. After adjusting for each individual's baseline body mass index (calculated as the weight in kilograms divided by the square of height in meters), depressed late adolescent girls were at a greater than 2-fold increased risk for obesity in adulthood compared with their non-depressed female peers (relative risk, 2.32; 95% confidence interval, 1.29-3.83). A dose-response relationship between the number of episodes of depression during adolescence, and risk for adult obesity was also observed in female subjects. The association was not observed for late adolescent boys or for early adolescent boys or girls.

Treatment of mixed states is typically based upon administration of mood stabilizing medication, which may include anticonvulsants such as valproic acid; atypical antipsychotics such as olanzapine, aripiprazole, and ziprasidone; or first-generation antipsychotics such as haloperidol. There is question of lithium's efficacy for treatment of mixed states due to conflicting conclusions drawn from various trials and research. Mood stabilizers work to reduce the manic symptoms associated with the mixed state, but they are not considered particularly effective for improving concurrent depressive symptoms.

The alleviation of dysphoria theory suggests that people with severe mental illness commonly have a negative self-image, which makes them vulnerable to using psychoactive substances to alleviate these feelings. Despite the existence of a wide range of dysphoric feelings (anxiety, depression, boredom, and loneliness), the literature on self-reported reasons for use seems to lend support for the experience of these feelings being the primary motivator for drug and alcohol misuse.

Neurocognitive disorders can have numerous causes: genetics, brain trauma, stroke, and heart issues. The main causes are neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease because they affect or deteriorate brain functions. Other diseases and conditions that cause NDCs include vascular dementia, frontotemporal degeneration, Lewy body disease, prion disease, normal pressure hydrocephalus, and dementia/neurocognitive issues due to HIV infection. They may also include dementia due to substance abuse or exposure to toxins.

Neurocongnitive disorder may also be caused by brain trauma, including concussions and Traumatic Brain Injuries, as well as post-traumatic stress and alcoholism. This is referred to as amnesia, and is characterized by damage to major memory encoding parts of the brain such as the hippocampus. Difficulty creating recent term memories is called anterograde amnesia and is caused by damage to the hippocampus part of the brain, which is a major part of the memory process. Retrograde amnesia is also caused by damage to the hippocampus, but the memories that were encoded or in the process of being encoded in long term memory are erased

Traditionally, a mixed affective state, formerly known as a mixed-manic or mixed episode, has been defined as a state wherein features unique to both depression and mania—such as despair, fatigue, morbid or suicidal ideation; racing thoughts, pressure of activity, and heightened irritability—occur either simultaneously or in very short succession.

Previously, the diagnostic criteria for both a manic and depressive episode had to be met in a consistent and sustained fashion, with symptoms enduring for at least a week (or any duration if psychiatric hospitalization was required), thereby restricting the official acknowledgement of mixed affective states to only a minority of patients with bipolar I disorder. In current (DSM-V) nomenclature, however, a "mixed episode" no longer stands as an episode of illness unto itself; rather, the symptomology specifier "with mixed features" can be applied to any major affective episode (manic, hypomanic, or depressive), meaning that they are now officially recognized in patients with, in addition to bipolar I disorder, bipolar II disorder and, by convention, major depressive disorder; a depressive mixed state in a patient, however, even in the absence of discrete periods of mania or hypomania, effectively rules out unipolar depression. Although convention dictates diagnosing such patients with major depressive disorder, it is more appropriate to classify such a patient as having an "Other Specified Bipolar or Related Disorder" and certainly following up such patients in the long-term, to ascertain the eventual appearance of an episode of mania or hypomania (with or without mixed features), which would prompt diagnostic revision. In those uncommon cases wherein the diagnostic criteria for both a manic and depressive episode are met, constituting what were heretofore classified as "mixed episodes", such a patient would be diagnosed as having a "manic episode with mixed features", because of the substantial social and occupational dysfunction inherent in such a state.

At risk mental state is the clinical presentation of those considered at risk of developing psychosis or schizophrenia. Such states were formerly considered treated as prodromes, emerging symptoms of psychosis, but this view is no longer prevalent as a prodromal period can not be confirmed unless the emergence of the condition has occurred.

The original specialist service for those with subclinical symptoms of psychosis was "The Pace Clinic" in Melbourne, Australia. Other clinics have since developed around the world.

There has been some considerable development of how the concept can be applied clinically.

Assessed during the structured interview developed by PACE.

In researching over 1000 individuals of vast range of backgrounds, Stompe and colleagues (2006) found that grandiosity remains as the second most common delusion after persecutory delusions. A variation in the occurrence of grandiosity delusions in schizophrenic patients across cultures has also been observed. In research done by Appelbaum "et al." it has been found that GDs appeared more commonly in patients with bipolar disorder (59%) than in patients with schizophrenia (49%), followed by presence in substance misuse disorder patients (30%) and depressed patients (21%).

A relationship has been claimed between the age of onset of bipolar disorder and the occurrence of GDs. According to Carlson "et al." (2000), grandiose delusions appeared in 74% of the patients who were 21 or younger at the time of the onset, while they occurred only in 40% of individuals 30 years or older at the time of the onset.

Delirium can be caused by the worsening of previous medical conditions, substance abuse or withdrawal, mental illness, severe pain, immobilization, sleep deprivation and hypnosis.

Other common causes that may increase the risk of delirium include infections of urinary tract, skin and stomach, pneumonia, old age, and poor nutrition.

Medical conditions associated with an increased risk of PTSD include cancer, heart attack, and stroke. Intensive-care unit (ICU) hospitalization is also a risk factor for PTSD. Some women experience PTSD from their experiences related to breast cancer and mastectomy.