Psychiatrists seek to provide a medical diagnosis of individuals by an assessment of symptoms, signs and impairment associated with particular types of mental disorder. Other mental health professionals, such as clinical psychologists, may or may not apply the same diagnostic categories to their clinical formulation of a client's difficulties and circumstances. The majority of mental health problems are, at least initially, assessed and treated by family physicians (in the UK general practitioners) during consultations, who may refer a patient on for more specialist diagnosis in acute or chronic cases.

Routine diagnostic practice in mental health services typically involves an interview known as a mental status examination, where evaluations are made of appearance and behavior, self-reported symptoms, mental health history, and current life circumstances. The views of other professionals, relatives or other third parties may be taken into account. A physical examination to check for ill health or the effects of medications or other drugs may be conducted. Psychological testing is sometimes used via paper-and-pen or computerized questionnaires, which may include algorithms based on ticking off standardized diagnostic criteria, and in rare specialist cases neuroimaging tests may be requested, but such methods are more commonly found in research studies than routine clinical practice.

Time and budgetary constraints often limit practicing psychiatrists from conducting more thorough diagnostic evaluations. It has been found that most clinicians evaluate patients using an unstructured, open-ended approach, with limited training in evidence-based assessment methods, and that inaccurate diagnosis may be common in routine practice. In addition, comorbidity is very common in psychiatric diagnosis, where the same person meets the criteria for more than one disorder. On the other hand, a person may have several different difficulties only some of which meet the criteria for being diagnosed. There may be specific problems with accurate diagnosis in developing countries.

More structured approaches are being increasingly used to measure levels of mental illness.

- HoNOS is the most widely used measure in English mental health services, being used by at least 61 trusts. In HoNOS a score of 0–4 is given for each of 12 factors, based on functional living capacity. Research has been supportive of HoNOS, although some questions have been asked about whether it provides adequate coverage of the range and complexity of mental illness problems, and whether the fact that often only 3 of the 12 scales vary over time gives enough subtlety to accurately measure outcomes of treatment.

Since the 1980s, Paula Caplan has been concerned about the subjectivity of psychiatric diagnosis, and people being arbitrarily “slapped with a psychiatric label.” Caplan says because psychiatric diagnosis is unregulated, doctors are not required to spend much time interviewing patients or to seek a second opinion. The Diagnostic and Statistical Manual of Mental Disorders can lead a psychiatrist to focus on narrow checklists of symptoms, with little consideration of what is actually causing the patient’s problems. So, according to Caplan, getting a psychiatric diagnosis and label often stands in the way of recovery.

In 2013, psychiatrist Allen Frances wrote a paper entitled "The New Crisis of Confidence in Psychiatric Diagnosis", which said that "psychiatric diagnosis… still relies exclusively on fallible subjective judgments rather than objective biological tests." Frances was also concerned about "unpredictable overdiagnosis." For many years, marginalized psychiatrists (such as Peter Breggin, Thomas Szasz) and outside critics (such as Stuart A. Kirk) have "been accusing psychiatry of engaging in the systematic medicalization of normality." More recently these concerns have come from insiders who have worked for and promoted the American Psychiatric Association (e.g., Robert Spitzer, Allen Frances). A 2002 editorial in the "British Medical Journal" warned of inappropriate medicalization leading to disease mongering, where the boundaries of the definition of illnesses are expanded to include personal problems as medical problems or risks of diseases are emphasized to broaden the market for medications.

PTED is a psychological adjustment-reactive disorder more severe than just being embittered in the colloquial sense. It can be qualitatively measured with high scientific reliability and repeatability. Related concepts include (ordinary) embitterment and reactive embitterment. Reactive embitterment may be specific, diffuse or non-PTED. Various ratings, assessment scales, and distinctions have been investigated.

There are no published or suggested studies on drug treatments for PTED. Selective serotonin reuptake inhibitors (SSRI's) are antidepressants like: Prozac, Paxil, Lexapro, Zoloft, Celexa, and Luvox. They have some benefit in PTED due to their antiobsessional properties. Anafranil, a TCA, is also used extensively.

Western doctors are more likely to diagnose it as a kind of stress or depression. The "Diagnostic and Statistical Manual of Mental Disorders" currently lists "hwabyeong" among its culture-bound illnesses. Outside of Korea, informally "hwabyeong" may be mistaken as a reference to a psychological profile marked by a short temper, or explosive, generally bellicose behavior. To the contrary, "hwabyeong" is a traditional psychological term used to refer to a condition characterized by passive suffering, is roughly comparable to depression, and is typically associated with older women. It is important that when diagnosing Hwabyeong, the culture of the patient is well understood. Since Hwabyeong can often be misdiagnosed as depression, the symptoms and culture need to be clearly and thoroughly looked into. Once Hwabyeong has been diagnosed, past treatments need to be reviewed. The treatments for the patient can then be a combination of pharmacological, and therapy-based interventions.

The treatment methods used to combat hwabyung include psychotherapy, drug treatment, family therapy, and community approaches. To be more successful psychiatrists might need to incorporate the teachings from traditional and religious healing methods or the use of han-puri, which is the sentiment of resolving, loosening, unraveling and appeasing negative emotions with positive ones. One example of hann-puri would be a mother who has suffered from poverty, less education, a violent husband, or a harsh mother-in-law, can be solved many years later by the success of her son for which she had endured hardships and sacrifices.

Despite recent initiatives to study psychopathology along dimensions of behavior and neurobiological indices, which would help refine a clearer picture of the development and treatment of externalizing disorders, the majority of research has examined specific mental disorders. Thus, best practices for many externalizing disorders are disorder-specific. For example, substance use disorders themselves are very heterogeneous and their best-evidenced treatment typically includes cognitive behavioral therapy, motivational interviewing, and a substance disorder-specific detoxification or psychotropic medication treatment component. The best-evidenced treatment for childhood conduct and externalizing problems more broadly, including youth with ADHD, ODD, and CD, is parent management training, a form of cognitive behavioral therapy. Additionally, individuals with ADHD, both youth and adults, are frequently treated with stimulant medications (or alternative psychotropic medications), especially if psychotherapy alone has not been effective in managing symptoms and impairment. Psychotherapy and medication interventions for individuals with severe, adult forms of antisocial behavior, such as antisocial personality disorder, have been mostly ineffective. An individual's comorbid psychopathology may also influences the course of treatment for an individual.

ADHD often precedes the onset of ODD, and approximately half of children with ADHD, Combined Type also have ODD. ODD is a risk factor for CD and frequently precedes the onset of CD symptoms. Children with an early onset of CD symptoms, with at least one symptom before age 10 years, are at risk for more severe and persistent antisocial behavior continuing into adulthood. Youth with early-onset conduct problems are particularly at risk for ASPD (note that an onset of CD prior to age 15 is part of the diagnostic criteria for ASPD), whereas CD is typically limited to adolescence when youth's CD symptoms begin during adolescence.

There is a considerable personality disorder diagnostic co-occurrence. Patients who meet the DSM-IV-TR diagnostic criteria for one personality disorder are likely to meet the diagnostic criteria for another. Diagnostic categories provide clear, vivid descriptions of discrete personality types but the personality structure of actual patients might be more accurately described by a constellation of maladaptive personality traits.

"Sites used DSM-III-R criterion sets. Data obtained for purposes of informing the development of the DSM-IV-TR personality disorder diagnostic criteria."

Abbreviations used: "PPD – Paranoid Personality Disorder, SzPD – Schizoid Personality Disorder, StPD – Schizotypal Personality Disorder, ASPD – Antisocial Personality Disorder, BPD – Borderline Personality Disorder, HPD – Histrionic Personality Disorder, NPD – Narcissistic Personality Disorder, AvPD – Avoidant Personality Disorder, DPD – Dependent Personality Disorder, OCPD – Obsessive-Compulsive Personality Disorder, PAPD – Passive-Aggressive Personality Disorder."

There are many different forms (modalities) of treatment used for personality disorders:

- Individual psychotherapy has been a mainstay of treatment. There are long-term and short-term (brief) forms.

- Family therapy, including couples therapy.

- Group therapy for personality dysfunction is probably the second most used.

- Psychological-education may be used as an addition.

- Self-help groups may provide resources for personality disorders.

- Psychiatric medications for treating symptoms of personality dysfunction or co-occurring conditions.

- Milieu therapy, a kind of group-based residential approach, has a history of use in treating personality disorders, including therapeutic communities.

- The practice of mindfulness that includes developing the ability to be nonjudgmentally aware of unpleasant emotions appears to be a promising clinical tool for managing different types of personality disorders.

There are different specific theories or schools of therapy within many of these modalities. They may, for example, emphasize psychodynamic techniques, or cognitive or behavioral techniques. In clinical practice, many therapists use an 'eclectic' approach, taking elements of different schools as and when they seem to fit to an individual client. There is also often a focus on common themes that seem to be beneficial regardless of techniques, including attributes of the therapist (e.g. trustworthiness, competence, caring), processes afforded to the client (e.g. ability to express and confide difficulties and emotions), and the match between the two (e.g. aiming for mutual respect, trust and boundaries).

Although exact rates of prevalence are not available, general population data shows a 0.002% prevalence over a year-long period and higher prevalence within clinical populations.

For individuals prescribed anti-anxiety medications such as Alprazolam (Xanax), caffeine can introduce further problems by increasing rates of cytotoxicity and cell death by necrosis. This leads to these medications being essentially ruled out as viable treatments for caffeine-induced anxiety. Due to caffeine’s negative interaction with anti-anxiety medications such as benzodiazepines, treatments for caffeine-induced anxiety disorder tend to focus on abstinence from or a reduction of caffeine intake and behavioral therapy. Some doctors may recommend a continuance of caffeine consumption but with the provision that the patient actively takes note of physiological changes that happen after caffeine intake. The goal of this approach is to help patients better understand the effects of caffeine on the body and to distinguish threatening symptoms from normal reactions.

Underlying causes may include:

- Han (a Korean culture-related depressive sentiment related to hard life and social unfairness resulting not only from a tragic collective national history, but also from personal traumas)

- prior instances of major depressive disorder

- prior instances of anxiety disorder

- prior instances of adjustment disorder

- prior instances of other somatoform disorders

- repression of feelings of anger/resentment arising from past events

Triggering causes are typically external events, including:

- familial stressors, e.g. spousal infidelity or conflict with in-laws

- witnessing acts/actions/phenomena that conflict with one's own moral and/or ethical principles

The syndrome itself is believed to be the result of the continued repression of feelings of anger without addressing their source. In holistic medicine the containment of anger in hwabyung disturbs the balance of the five bodily elements, resulting in the development of psychosomatic symptoms such as panic, insomnia, and depression after a long period of repressed feelings.

It is possible that hormonal imbalances such as those around the time of menopause may also be an underlying cause of hwabyung in middle-aged women, the most often-diagnosed demographic.

This disorder may resolve itself with time or may develop into a more severe disorder such as PTSD. However, results of Creamer, O'Donnell, and Pattison's (2004) study of 363 patients suggests that a diagnosis of acute stress disorder had only limited predictive validity for PTSD. Creamer et al. did find that re-experiences of the traumatic event and arousal were better predictors of PTSD. Early pharmacotherapy may prevent the development of posttraumtic symptoms.

Studies have been conducted to assess the efficacy of counselling and psychotherapy for people with ASD. Cognitive behavioral therapy which included exposure and cognitive restructuring was found to be effective in preventing PTSD in patients diagnosed with ASD with clinically significant results at 6 months follow-up. A combination of relaxation, cognitive restructuring, imaginal exposure, and in vivo exposure was superior to supportive counseling. Mindfulness based stress reduction programs also appear to be effective for stress management.

In a wilderness context where counseling, psychotherapy, and cognitive behavioral therapy is unlikely to be available, the treatment for acute stress reaction is very similar for the treatment of cardiogenic shock, vascular shock, and hypovolemic shock; that is, allowing the patient to lie down, providing reassurance, and removing the stimulus for the occurrence of the reaction. In traditional shock cases, this is generally the relieving of pain from injuries or the stopping of blood loss. In an acute stress reaction, this may be pulling a rescuer away from the emergency to calm down, or blocking the sight of an injured friend from a patient.

In 2013, the American Psychiatric Association released the fifth edition of the DSM (DSM-5). To be diagnosed with schizophrenia, two diagnostic criteria have to be met over much of the time of a period of at least one month, with a significant impact on social or occupational functioning for at least six months. The person had to be suffering from delusions, hallucinations, or disorganized speech. A second symptom could be negative symptoms, or severely disorganized or catatonic behaviour. The definition of schizophrenia remained essentially the same as that specified by the 2000 version of DSM (DSM-IV-TR), but DSM-5 makes a number of changes.

- Subtype classifications – such as catatonic and paranoid schizophrenia – are removed. These were retained in previous revisions largely for reasons of tradition, but had subsequently proved to be of little worth.

- Catatonia is no longer so strongly associated with schizophrenia.

- In describing a person's schizophrenia, it is recommended that a better distinction be made between the current state of the condition and its historical progress, to achieve a clearer overall characterization.

- Special treatment of Schneider's first-rank symptoms is no longer recommended.

- Schizoaffective disorder is better defined to demarcate it more cleanly from schizophrenia.

- An assessment covering eight domains of psychopathology – such as whether hallucination or mania is experienced – is recommended to help clinical decision-making.

The ICD-10 criteria are typically used in European countries, while the DSM criteria are used in the United States and to varying degrees around the world, and are prevailing in research studies. The ICD-10 criteria put more emphasis on Schneiderian first-rank symptoms. In practice, agreement between the two systems is high. The current proposal for the ICD-11 criteria for schizophrenia recommends adding self-disorder as a symptom.

If signs of disturbance are present for more than a month but less than six months, the diagnosis of schizophreniform disorder is applied. Psychotic symptoms lasting less than a month may be diagnosed as brief psychotic disorder, and various conditions may be classed as psychotic disorder not otherwise specified, while schizoaffective disorder is diagnosed if symptoms of mood disorder are substantially present alongside psychotic symptoms. If the psychotic symptoms are the direct physiological result of a general medical condition or a substance, then the diagnosis is one of a psychosis secondary to that condition. Schizophrenia is not diagnosed if symptoms of pervasive developmental disorder are present unless prominent delusions or hallucinations are also present.

Schizophrenia is diagnosed based on criteria in either the American Psychiatric Association's (APA) fifth edition of the "Diagnostic and Statistical Manual of Mental Disorders" (DSM 5), or the World Health Organization's International Statistical Classification of Diseases and Related Health Problems (ICD-10). These criteria use the self-reported experiences of the person and reported abnormalities in behavior, followed by a clinical assessment by a mental health professional. Symptoms associated with schizophrenia occur along a continuum in the population and must reach a certain severity and level of impairment, before a diagnosis is made. As of 2013 there is no objective test.

It is difficult to gain an accurate picture of incidence and prevalence of self-harm. This is due in a part to a lack of sufficient numbers of dedicated research centres to provide a continuous monitoring system. However, even with sufficient resources, statistical estimates are crude since most incidences of self-harm are undisclosed to the medical profession as acts of self-harm are frequently carried out in secret, and wounds may be superficial and easily treated by the individual. Recorded figures can be based on three sources: psychiatric samples, hospital admissions and general population surveys.

The World Health Organization estimates that, as of 2010, 880,000 deaths occur as a result of self-harm. About 10% of admissions to medical wards in the UK are as a result of self-harm, the majority of which are drug overdoses. However, studies based only on hospital admissions may hide the larger group of self-harmers who do not need or seek hospital treatment for their injuries, instead treating themselves. Many adolescents who present to general hospitals with deliberate self-harm report previous episodes for which they did not receive medical attention. In the United States up to 4% of adults self-harm with approximately 1% of the population engaging in chronic or severe self-harm.

Current research suggests that the rates of self-harm are much higher among young people with the average age of onset between 14 and 24. The earliest reported incidents of self-harm are in children between 5 and 7 years old. In the UK in 2008 rates of self-harm in young people could be as high as 33%. In addition there appears to be an increased risk of self-harm in college students than among the general population. In a study of undergraduate students in the US, 9.8% of the students surveyed indicated that they had purposefully cut or burned themselves on at least one occasion in the past. When the definition of self-harm was expanded to include head-banging, scratching oneself, and hitting oneself along with cutting and burning, 32% of the sample said they had done this. In Ireland, a study found that instances of hospital-treated self-harm were much higher in city and urban districts, than in rural settings. The CASE (Child & Adolescent Self-harm in Europe) study suggests that the life-time risk of self-injury is ~1:7 for women and ~1:25 for men.

There is considerable uncertainty about which forms of psychosocial and physical treatments of people who harm themselves are most effective. Psychiatric and personality disorders are common in individuals who self-harm and as a result self-harm may be an indicator of depression and/or other psychological problems. Many people who self-harm have moderate or severe depression and therefore treatment with antidepressant medications may often be used. There is tentative evidence for the medication flupentixol; however, greater study is required before it can be recommended.

There must be a clear temporal connection between the impact of an exceptional stressor and the onset of symptoms; onset is usually within a few minutes or days but may occur up to one month after the stressor. In addition, the symptoms show a mixed and usually changing picture; in addition to the initial state of "daze," depression, anxiety, anger, despair, overactivity, and withdrawal may all be seen, but no one type of symptom predominates for long; the symptoms usually resolve rapidly in those cases where removal from the stressful environment is possible; in cases where the stress continues or cannot by its nature be reversed, the symptoms usually begin to diminish after 24–48 hours and are usually minimal after about 3 days.

In the second edition of the Chinese Classification of Mental Disorders (CCMD-2) published by the Chinese Society of Psychiatry the diagnosis of “Qigong Deviation Syndrome” is based upon the following criteria:

- The subject being demonstrably normal before doing qigong exercises

- Psychological and physiological reactions appearing during or after qigong exercises (suggestion and autosuggestion may play an important role in these reactions)

- Complaints of abnormal sensations during or after qigong exercises

- Diagnostic criteria do not meet other mental disorders such as schizophrenia, affective disorder, and neurosis.

Treatment of secondary forms of delusional parasitosis are addressed by treating the primary associated psychological or physical condition. The primary form is treated much as other delusional disorders and schizophrenia. In the past, pimozide was the drug of choice when selecting from the typical antipsychotics. Currently, atypical antipsychotics such as olanzapine or risperidone are used as first line treatment.

However, it is also characteristic that sufferers will reject the diagnosis of delusional parasitosis by medical professionals, and very few are willing to be treated, despite demonstrable efficacy of treatment.

Zou huo ru mo (走火入魔) or "qigong deviation" (气功出偏), is a Chinese term traditionally used to indicate that something has gone wrong in spiritual or martial arts training, applied to describe a physiological or psychological disorder believed to result during or after qigong practice, believed by the qigong community to result from "improper practice" of qigong and other self-cultivation techniques, and highlighted in the social and political context of mass popularization of qigong in China.

Secondary organic delusional parasitosis occurs when the state of the patient is caused by a medical illness or substance (medical or recreational) use. In the DSM-IV this corresponds with "psychotic disorder due to general medical condition". Physical illnesses that can underlie secondary organic delusional parasitosis include: hypothyroidism, cancer, cerebrovascular disease, tuberculosis, neurological disorders, vitamin B12 deficiency, and diabetes mellitus. Any illness or medication for which formication is a symptom or side effect can become a trigger or underlying cause of delusional parasitosis.

Other physiological factors which can cause formication and thus can sometimes lead to this condition include: menopause (i.e. hormone withdrawal); allergies, and drug abuse, including but not limited to cocaine and methamphetamine (as in amphetamine psychosis). It appears that many of these physiological factors, as well as environmental factors such as airborne irritants, are capable of inducing a "crawling" sensation in otherwise healthy individuals; however, some people become fixated on the sensation and its possible meaning, and this fixation may then develop into delusional parasitosis.

Frank Tallis, a researcher in the topic of love and lovesickness, suggests in his 2005 article that lovesickness occurs when one is “truly, madly, deeply” in love and should be taken more seriously by medical professionals. Similarly, health experts agree that lovesickness has been known to kill and the diagnosis process should be taken more seriously. Symptoms of lovesickness are usually misdiagnosed for various other diseases or mental health issues such as OCD, this is because love sickness is less commonly recognized as a mental health issue in itself even though lovesickness is an extremely common, widespread disease.

Tallis includes a list of common symptoms of love sickness:

- Mania - an abnormally elevated mood or inflated self-esteem

- Depression

- Nausea

- Tearfulness

- Insomnia, which may lead to fatigue

- Lack of concentration

- Loss of appetite or overeating

- Hopelessness and/or helplessness

- Stress - high blood pressure, pain in chest and heart, acute insomnia; sometimes brought on by a "crush"

- Obsessive-Compulsive disorder - Preoccupation and hoarding valueless but superstitiously resonant items

- Psychologically created physical symptoms, such as upset stomach, change in appetite, insomnia, dizziness, and confusion

- Chronic neck pain, body tremors, intrusive thoughts, frequent flashbacks.

- Rapid mood swings

According to Tallis, many symptoms of being lovesick can be categorized under the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders) and the ICD-10 (International Classification of Diseases). Obsessive-Compulsive disorder (OCD) is a symptom of lovesickness because it includes a preoccupation, this would include constantly checking one's cellphone, Facebook, the hoarding of valueless items, etc. A further study conducted by Italian Psychiatrist Donatella Marazitti found that when people fall in love their estimated serotonin levels drop to levels found in patients with OCD, this level is significantly lower than that of an average or healthy person.

A neurological disorder is any disorder of the nervous system. Structural, biochemical or electrical abnormalities in the brain, spinal cord or other nerves can result in a range of symptoms. Examples of symptoms include paralysis, muscle weakness, poor coordination, loss of sensation, seizures, confusion, pain and altered levels of consciousness. There are many recognized neurological disorders, some relatively common, but many rare. They may be assessed by neurological examination, and studied and treated within the specialities of neurology and clinical neuropsychology.

Interventions for neurological disorders include preventative measures, lifestyle changes, physiotherapy or other therapy, neurorehabilitation, pain management, medication, or operations performed by neurosurgeons. The World Health Organization estimated in 2006 that neurological disorders and their sequelae (direct consequences) affect as many as one billion people worldwide, and identified health inequalities and social stigma/discrimination as major factors contributing to the associated disability and suffering.

According to Child and Adolescent Mental Health, approximately 5 percent of children suffer from specific phobias and 15 percent seek treatment for anxiety-related problems. In recent years the number of children with clinically diagnosed phobias has gradually increased. Researchers are finding that the majority of these diagnoses come anxiety related phobias or society phobias.

Specific phobias are more prevalent in girls than in boys. Likewise, specific phobias are also more prevalent in older children than younger.