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.

Lithium and the anticonvulsants carbamazepine, lamotrigine, and valproic acid are used as mood stabilizers to treat bipolar disorder. These mood stabilizers are used for long-term mood stabilization but have not demonstrated the ability to quickly treat acute bipolar depression. Lithium is preferred for long-term mood stabilization. Carbamazepine effectively treats manic episodes, with some evidence it has greater benefit in rapid-cycling bipolar disorder, or those with more psychotic symptoms or a more schizoaffective clinical picture. It is less effective in preventing relapse than lithium or valproate. Since then, valproate has become a commonly prescribed treatment, and is effective in treating manic episodes. Lamotrigine has some efficacy in treating bipolar depression, and this benefit is greatest in more severe depression. It has also been shown to have some benefit in preventing bipolar disorder relapses, though there are concerns about the studies done, and is of no benefit in rapid cycling subtype of bipolar disorder. The effectiveness of topiramate is unknown.

Antipsychotic medications are effective for short-term treatment of bipolar manic episodes and appear to be superior to lithium and anticonvulsants for this purpose. Atypical antipsychotics are also indicated for bipolar depression refractory to treatment with mood stabilizers. Olanzapine is effective in preventing relapses, although the supporting evidence is weaker than the evidence for lithium.

In most cases hospital admission is necessary. Antipsychotic drugs and mood stabilizing drugs such as lithium are typically administered but is not clear if mood stabilizers can be titrated to a high enough level quickly enough to be effective. Electroconvulsive therapy may be considered, especially if there is a high risk of suicide.

Family support may be provided via a social worker.

A 2010 review by the Cochrane collaboration found that no medications show promise for "the core BPD symptoms of chronic feelings of emptiness, identity disturbance and abandonment". However, the authors found that some medications may impact isolated symptoms associated with BPD or the symptoms of comorbid conditions. A 2017 review examined evidence published since the 2010 Cochrane review and found that "evidence of effectiveness of medication for BPD remains very mixed and is still highly compromised by suboptimal study design".

Of the typical antipsychotics studied in relation to BPD, haloperidol may reduce anger and flupenthixol may reduce the likelihood of suicidal behavior. Among the atypical antipsychotics, one trial found that aripiprazole may reduce interpersonal problems and impulsivity. Olanzapine may decrease affective instability, anger, psychotic paranoid symptoms, and anxiety, but a placebo had a greater ameliorative impact on suicidal ideation than olanzapine did. The effect of ziprasidone was not significant.

Of the mood stabilizers studied, valproate semisodium may ameliorate depression, interpersonal problems, and anger. Lamotrigine may reduce impulsivity and anger; topiramate may ameliorate interpersonal problems, impulsivity, anxiety, anger, and general psychiatric pathology. The effect of carbamazepine was not significant. Of the antidepressants, amitriptyline may reduce depression, but mianserin, fluoxetine, fluvoxamine, and phenelzine sulfate showed no effect. Omega-3 fatty acid may ameliorate suicidality and improve depression. As of 2017, trials with these medications had not been replicated and the effect of long-term use had not been assessed.

Because of weak evidence and the potential for serious side effects from some of these medications, the UK National Institute for Health and Clinical Excellence (NICE) 2009 clinical guideline for the treatment and management of BPD recommends, "Drug treatment should not be used specifically for borderline personality disorder or for the individual symptoms or behavior associated with the disorder." However, "drug treatment may be considered in the overall treatment of comorbid conditions". They suggest a "review of the treatment of people with borderline personality disorder who do not have a diagnosed comorbid mental or physical illness and who are currently being prescribed drugs, with the aim of reducing and stopping unnecessary drug treatment".

Long-term psychotherapy is currently the treatment of choice for BPD. While psychotherapy, in particular dialectical behavior therapy and psychodynamic approaches, is effective, the effects are small.

More rigorous treatments are not substantially better than less rigorous treatments. There are six such treatments available: dynamic deconstructive psychotherapy (DDP), mentalization-based treatment (MBT), transference-focused psychotherapy, dialectical behavior therapy (DBT), general psychiatric management, and schema-focused therapy. While DBT is the therapy that has been studied the most, all these treatments appear effective for treating BPD, except for schema-focused therapy. Long-term therapy of any kind, including schema-focused therapy, is better than no treatment, especially in reducing urges to self-injure.

Cognitive behavioral therapy (CBT) is also a type of psychotherapy used for treatment of BPD. This type of therapy relies on changing people's behaviors and beliefs by identifying problems from the disorder. CBT is known to reduce some anxiety and mood symptoms as well as reduce suicidal thoughts and self-harming behaviors.

Mentalization-based therapy and transference-focused psychotherapy are based on psychodynamic principles, and dialectical behavior therapy is based on cognitive-behavioral principles and mindfulness. General psychiatric management combines the core principles from each of these treatments, and it is considered easier to learn and less intensive. Randomized controlled trials have shown that DBT and MBT may be the most effective, and the two share many similarities. Researchers are interested in developing shorter versions of these therapies to increase accessibility, to relieve the financial burden on patients, and to relieve the resource burden on treatment providers.

From a psychodynamic perspective, a special problem of psychotherapy with people with BPD is intense projection. It requires the psychotherapist to be flexible in considering negative attributions by the patient rather than quickly interpreting the projection.

Some research indicates that mindfulness meditation may bring about favorable structural changes in the brain, including changes in brain structures that are associated with BPD. Mindfulness-based interventions also appear to bring about an improvement in symptoms characteristic of BPD, and some clients who underwent mindfulness-based treatment no longer met a minimum of five of the DSM-IV-TR diagnostic criteria for BPD.

For women taking psychiatric medication, the decision as to whether continue during pregnancy and whether to take them while breast feeding is difficult in any case; there is no data to guide this decision with respect to preventing postpartum psychosis. There is no data to guide a decision as to whether women at high risk for postpartum psychosis should take antipsychotic medicine to prevent it. For women at risk of postpartum psychosis, informing medical care-givers, and monitoring by a psychiatrist during pregnancy, in the perinatal period, and for a few weeks following delivery, is recommended.

For women with known bipolar disorder, taking medication during pregnancy roughly halves the risk of a severe postpartum episode, as does starting to take medication immediately after the birth.

Folie à deux (; ; French for "madness of two"), or shared psychosis, is a psychiatric syndrome in which symptoms of a delusional belief and sometimes hallucinations are transmitted from one individual to another. The same syndrome shared by more than two people may be called "folie à trois", "folie à quatre", "folie en famille" ("family madness"), or even "folie à plusieurs" ("madness of many").

Recent psychiatric classifications refer to the syndrome as shared psychotic disorder (DSM-IV – 297.3) and induced delusional disorder (F24) in the ICD-10, although the research literature largely uses the original name. This disorder is not in the current DSM (DSM-5). The disorder was first conceptualized in 19th-century French psychiatry by Charles Lasègue and Jean-Pierre Falret and is also known as Lasègue-Falret syndrome.

This syndrome is most commonly diagnosed when the two or more individuals concerned live in proximity and may be socially or physically isolated and have little interaction with other people. Various sub-classifications of "folie à deux" have been proposed to describe how the delusional belief comes to be held by more than one person :

- Folie imposée is where a dominant person (known as the 'primary', 'inducer' or 'principal') initially forms a delusional belief during a psychotic episode and imposes it on another person or persons (known as the 'secondary', 'acceptor' or 'associate') with the assumption that the secondary person might not have become deluded if left to his or her own devices. If the parties are admitted to hospital separately, then the delusions in the person with the induced beliefs usually resolve without the need of medication.

- Folie simultanée describes either the situation where two people considered to suffer independently from psychosis influence the content of each other's delusions so they become identical or strikingly similar, or one in which two people "morbidly predisposed" to delusional psychosis mutually trigger symptoms in each other.

Folie à deux and its more populous cousins are in many ways a psychiatric curiosity. The current Diagnostic and Statistical Manual of Mental Disorders states that a person cannot be diagnosed as being delusional if the belief in question is one "ordinarily accepted by other members of the person's culture or subculture" (see entry for delusion). It is not clear at what point a belief considered to be delusional escapes from the "folie à..." diagnostic category and becomes legitimate because of the number of people holding it. When a large number of people may come to believe obviously false and potentially distressing things based purely on hearsay, these beliefs are not considered to be clinical delusions by the psychiatric profession and are labelled instead as mass hysteria.

Clinical lycanthropy is a rare condition and is largely considered to be an idiosyncratic expression of a psychotic episode caused by another condition such as schizophrenia, bipolar disorder or clinical depression.

However, there are suggestions that certain neurological conditions and cultural influences may result in the expression of the human-animal transformation theme that defines the condition.

One important factor may be differences or changes in parts of the brain known to be involved in representing body shape (e.g., see proprioception and body image). A neuroimaging study of two people diagnosed with clinical lycanthropy showed that these areas display unusual activation, suggesting that when people report their bodies are changing shape, they may be genuinely perceiving those feelings.

Boanthropy is a psychological disorder in which a human believes himself or herself to be a bovine.

A fixed fantasy — also known as a "dysfunctional schema" — is a belief or system of beliefs held by a single individual to be genuine, but that cannot be verified in reality. The term is typically applied to individuals suffering from some type of psychiatric dysregulation, most often a personality disorder.

The term is also used in the different context of psychoanalysis to distinguish between 'a normal transitory one and a fixed fantasy' with respect to the phantasised 'fulfilment in conscious or unconscious thought of the sexualised wish'.

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.

For most balance and gait disorders, some form of displacement exercise is thought helpful (for example walking, jogging, or bicycling but not on a treadmill or stationary bicycle). This has not been well-studied in MdDS. Medications that suppress the nerves and brain circuits involved in balance (for example, the benzodiazepine clonazepam) have been noted to help and can lower symptoms, but it is not a cure. It is not known whether medication that suppress symptoms prolongs symptom duration or not. Vestibular therapy has not proved to be effective in treating MdDS.

Additional research is being undertaken into the neurological nature of this syndrome through imaging studies. The disorder remains incurable and permanent if the symptoms do not remit in a short period of time.

The most famous sufferer of this disorder is claimed to be Nebuchadnezzar II, who in the Book of Daniel "was driven from men, and did eat grass as oxen". Most probably, the authors were making fun of his aversion to meat or violence.

Carl Jung would subsequently instance 'Nebuchadnezzar...[as] a complete regressive degeneration of a man who has overreached himself'.

According to Persian traditions, the Buyid prince Majd al-Dawla was suffering from an illusion that he is a cow, making the sound of a cow and asking that to be killed so that his flesh could be consumed. He was cured by Avicenna.

The term refers simplistically to a thought disorder shown from speech with a lack of observance to the main subject of discourse, such that a person whilst speaking on a topic deviates from the topic. Further definition is of speech that deviates from an answer to a question that is relevant in the first instance but deviates from the relevancy to related subjects not involved in a direct answering of the question. In the context of a conversation or discussion the communication is a response that is ineffective in that the form is inappropriate for adequate understanding. The person's speech seems to indicate that their attention to their own speech has perhaps in some way been overcome during the occurrence of cognition whilst speaking, causing the vocalized content to follow thought that is apparently without reference to the original idea or question; or the person's speech is considered evasive in that the person has decided to provide an answer to a question that is an avoidance of a direct answer.

Studies of borderline children often uncovered at the base of their self-destructive behaviour patterns ' a "fixed fantasy"...a rigid, nonreflective scenario of self-induced pain'. As part of a psychic defence mechanism, 'the omnipotence betrayed by the "fixed fantasy" underlying self-victimization or other forms of self-defeating behaviour...creates the illusory sense that they are actively producing the abandonment [&] pain', rather than merely suffering it passively - 'arranging deceits..arrang[ing] for blows to fall'. Unfortunately 'in the course of development, these patterns acquire multiple adaptive functions...and serve as a key organizer of their sense of self'.

'In producing movement away from fixed fantasy systems, commonplace statements are often necessary because the more fixed and extensive the fantasy system, the fewer the transitional opportunities offered; there is little conflicting material to ride. Banalities may be the only resource', as anything more complex may be used to feed back into the fantasy system itself.

Tangentiality as a medical symptom is a physical symptom observed in speech that tends to occur in situations where a person is experiencing high anxiety, as a manifestation of the psychosis known as "schizophrenia", in dementia or in states of delirium.

In medicine, a prodrome is an early sign or symptom (or set of signs and symptoms), which often indicate the onset of a disease before more diagnostically specific signs and symptoms develop. It is derived from the Greek word "prodromos", meaning "running before". Prodromes may be non-specific symptoms or, in a few instances, may clearly indicate a particular disease, such as the prodromal migraine aura.

For example, fever, malaise, headache and lack of appetite frequently occur in the prodrome of many infective disorders. A prodrome can be the early precursor to an episode of a chronic neurological disorder such as a migraine headache or an epileptic seizure, where prodrome symptoms may include euphoria or other changes in mood, insomnia, abdominal sensations, disorientation, aphasia, or photosensitivity. Such a prodrome occurs on a scale of days to an hour before the episode, where an aura occurs more immediate to it.

Prodromal labour, mistakenly called "false labour," refers to the early signs before labour starts.

A spectrum disorder is a mental disorder that includes a range of linked conditions, sometimes also extending to include singular symptoms and traits. The different elements of a spectrum either have a similar appearance or are thought to be caused by the same underlying mechanism. In either case, a spectrum approach is taken because there appears to be "not a unitary disorder but rather a syndrome composed of subgroups". The spectrum may represent a range of severity, comprising relatively "severe" mental disorders through to relatively "mild and nonclinical deficits".

In some cases, a spectrum approach joins together conditions that were previously considered separately. A notable example of this trend is the autism spectrum, where conditions on this spectrum may now all be referred to as autism spectrum disorders. In other cases, what was treated as a single disorder comes to be seen (or seen once again) as comprising a range of types, a notable example being the bipolar spectrum. A spectrum approach may also expand the type or the severity of issues which are included, which may lessen the gap with other diagnoses or with what is considered "normal". Proponents of this approach argue that it is in line with evidence of gradations in the type or severity of symptoms in the general population, and helps reduce the stigma associated with a diagnosis. Critics, however, argue that it can take attention and resources away from the most serious conditions associated with the most disability, or on the other hand could unduly medicalize problems which are simply challenges people face in life.

Factitious disorder imposed on another, also known as Munchausen syndrome by proxy (MSbP), is a condition where a caregiver or spouse fabricates, exaggerates, or induces mental or physical health problems in those who are in their care, with the primary motive of gaining attention or sympathy from others. The name is derived from the term Munchausen syndrome, a psychiatric factitious disorder wherein those affected feign disease, illness, or psychological trauma to draw attention, sympathy, or reassurance to themselves. However, unlike Munchausen syndrome, in MSbP, the deception involves not themselves, but rather someone under the person's care. MSbP is primarily distinguished from other forms of abuse or neglect by the motives of the perpetrator. Some experts consider it to be an elusive, potentially lethal, and frequently misunderstood form of child abuse or medical neglect. However, others consider the concept to be problematic, since it is based largely on supposition regarding a person's motives, which can be open to radically different interpretations.

Factitious disorder imposed on another has also spawned much heated controversy within the legal and social services communities. In a handful of high-profile cases, mothers who have had several children die from sudden infant death syndrome have been declared to have MSbP. Based on MSbP testimony of an expert witness, they were tried for murder, convicted, and imprisoned for several years. In some cases, that testimony was later impeached, resulting in exoneration of those defendants.

A prodrome for schizophrenia is the period of decreased cognitive functioning that is postulated to correlate with the onset of psychotic symptoms. The concept has been reconsidered as the pathways to emerging psychosis have been investigated since the mid-1990s. One example of the international paradigms aimed at researching the prodrome is the North American Prodrome Longitudinal Study (NAPLS). This study is concerned with brain development, hormones, and neuropsychological functions that may play a role in risk for and prevention of mental illness in young adulthood. The term at risk mental state is sometimes preferred, as a prodromal period cannot be confirmed unless the emergence of the condition has occurred. (Also see early psychosis.)

Prodrome, or psychosis risk syndrome as it is also known, is a proposed syndrome to be used in the "DSM-5" (2013) of psychiatry. It is also defined as "the aura that precedes a psychotic break by up to two or three years." Patients with this condition "still have 'insight' – a pivotal word in psychiatric literature, indicating that a patient can still recognize an altered worldview as a sign of illness, and not a revelation." Prodrome is also sometimes called "attenuated psychotic symptoms syndrome." Chairman of the DSM-IV Task Force, Allen Frances, has criticised the concept of Psychosis Risk Syndrome on the grounds of a high rate of inaccuracy, the potential to stigmatize young people given this label, the lack of any effective treatment, and the risk of children and adolescents being given dangerous antipsychotic medication.

About one third of patients with prodrome are diagnosed with schizophrenia or other psychosis in a few years. In the North American Prodrome Longitudinal Study, researchers found that 35 percent of "patients had a psychotic break within two and a half years of enrolling at a clinic." 65 percent "found that their symptoms passed or plateaued." A psychotic break is made statistically more likely (43% vs. 35%) if the patient abuses certain drugs.

No treatment has yet proven effective. Most treatment options have focused on reducing complications (such as cardiovascular disease) with coronary artery bypass surgery and low-dose aspirin.

Growth hormone treatment has been attempted. The use of Morpholinos has also been attempted in mice and cell cultures in order to reduce progerin production. Antisense Morpholino oligonucleotides specifically directed against the mutated exon 11–exon 12 junction in the mutated pre-mRNAs were used.

A type of anticancer drug, the farnesyltransferase inhibitors (FTIs), has been proposed, but their use has been mostly limited to animal models. A Phase II clinical trial using the FTI lonafarnib began in May 2007. In studies on the cells another anti-cancer drug, rapamycin, caused removal of progerin from the nuclear membrane through autophagy. It has been proved that pravastatin and zoledronate are effective drugs when it comes to the blocking of farnesyl group production.

Farnesyltransferase inhibitors (FTIs) are drugs that inhibit the activity of an enzyme needed in order to make a link between progerin proteins and farnesyl groups. This link generates the permanent attachment of the progerin to the nuclear rim. In progeria, cellular damage can occur because that attachment takes place and the nucleus is not in a normal state. Lonafarnib is an FTI, which means it can avoid this link, so progerin can not remain attached to the nucleus rim and it now has a more normal state.

Studies of sirolimus, an mTOR Inhibitor, demonstrate that it can minimize the phenotypic effects of progeria fibroblasts. Other observed consequences of its use are: abolishment of nuclear blebbing, degradation of progerin in affected cells and reduction of insoluble progerin aggregates formation. These results have been observed only "in vitro" and are not the results of any clinical trial, although it is believed that the treatment might benefit HGPS patients.

The delivery of lonafarnib is not approved by the US Food and Drug Administration (FDA). Therefore, it can only be used in certain clinical trials. Until treatment with FTIs is thoroughly tested in progeria children in clinical trials, its effects on humans cannot be known, although its effects on mice seem to be positive. A 2012 clinical trial found that it improved weight gain and other symptoms of progeria.

At least one clinical trial on readaptation of the vestibulo-ocular reflex undertaken by Dr Mingjia Dai from Mount Sinai Hospital in New York City has produced results for a significant percentage of patients who have participated in the program.

Dai has developed an intervention that provided improvement in symptoms for 70% of the patients in the clinical trial phase. The protocol involves a physical manipulation of the patient intended to readapt the vestibulo-ocular reflex. While the program is no longer in the research phase, Dai continues to accept patients. According to Dai, "success" is measured as a 50% reduction of symptoms.

Recent research reveals a very small percentage of MdDS cases may be related to optokinetic nystagmus (OKN).