HCV is one of the few infections, in addition to HIV, which is heavily linked to psychiatric disorders (
40,
41).A cause for this strong association is that illicit drug injection (IDU) is the most important risk factor for HCV infection. Drug injection is common in the patients with personality problems, besides other high risk behaviors (alcoholism, sexual high risk behaviors), and mood disorders (
42). Even among non-injection drug users, up to 30% might be infected with HCV (
43). Among all abused substances alcohol is the only one that can boost the progression of the liver involvement and therefore should be taken very seriously. United States veterans have been most widely studied regarding the prevalence of trimorbidity (HCV, substance abuse and psychiatric illness). In the largest study on veterans, 85% of 33842 tested individuals had evidence of past or present psychiatric disorders or substance abuse, and more than 60% of them had comorbid substance abuse and psychiatric disorders (
44). However, in non-veteran patients the rates of psychiatric disorders have been much lower (
45,
46). Alcoholism is associated with higher prevalence of anti-HCV antibody positivity. Alcohol acts synergistically with HCV to deteriorate the liver disease and reduces the treatment response to Interferon (IFN) primarily by decreasing the compliance (
47). IFN-alpha is increasingly being used for HCV treatment. Besides its beneficial effects, IFN alpha may induce a variety of neuropsychiatric side effects such as acute confusional state, depressive syndrome, and agitated manic episode (
48). Following IFN treatment of patients with HCV, up to 70% may develop depression (
41). Several mechanisms have been proposed for this association including altered monoamine metabolism (
41), increased rate of apoptosis (
49), BDNF reduction (
50), and altered hypothalamus-pituitary-adrenal axis function (
48). In a meta-analysis of 26 observational studies, the authors concluded that one fourth of patients who underwent treatment with interferon and ribavirin, developed major depressive disorder (MDD). High baseline serum interleukin 6 concentrations, being female, history of psychiatric disorder, sub-threshold depressive symptoms, and low educational level significantly predicted the occurrence of MDD during antiviral treatment (
51). Neuro-vegetative/somatic symptoms of depression occur early in the course of IFN therapy, whereas cognitive/mood symptoms often become evident after the fourth week of treatment (
41). Depression, anxiety, and cognitive complaints are responsive to serotonergic antidepressants, whereas neuro-vegetative symptoms such as decreased appetite, fatigue, sexual impairment, and psychosomatic symptoms are less responsive to SSRIs (
52). Neurovegetative symptoms can be better managed with serotonin-norepinephrine reuptake inhibitors, bupropion, methylphenidate or modafinil (
48). In a systematic review of 64 observational and interventional studies, the authors showed that SSRIs might be the first choice for treatment of interferon-induced MDD (
53). IFN alpha-induced acute confusional states present with psychomotor retardation, disorientation, Parkinsonism, and psychosis. IFN alpha is also capable of inducing manic symptoms. Severe mania which can occur as a result of IFN administration should be treated with immediate discontinuation of IFN and antidepressants and initiation of a mood stabilizer (
48). A recent retrospective study on 910 patients with HCV compared the rate of psychiatric complications during the treatment with IFN between patients with bipolar disorder, patients with MDD, and patients without psychiatric illness. Psychiatric complications occurred in more than half of the patients with MDD or bipolar disorder and one third of the patients without psychiatric illness. However manic episode occurred only in one out of 38 patients with bipolar disorder. Therefore, it was concluded that patients with bipolar disorder who were selected carefully can achieve successful treatment outcomes comparable to those in patients without bipolar disorder (
54). Specific risk factors for IFN-induced suicide are unknown yet (
41) . European Expert Consensus Statement has recently released a guideline for management of mental health disturbances associated with IFN treatment. According to the Consensus, before starting the antiviral treatment, a complete psychiatric history should be taken, and information regarding psychiatric adverse effects should be given. Following initiation of the antiviral treatment, mood status should be assessed every four weeks in the first three months of treatment and then at least every 12 weeks after the end of the treatment. The intervals between two monitoring visits should be halved in the case of psychiatric comorbidity or substance abuse. Patients with psychiatric comorbidity or substance abuse do not generally differ in their treatment outcomes from other patients. However, the Consensus suggested acute and major psychiatric disorders and acute ongoing and uncontrolled IV drug abuse as relative contraindications to antiviral treatment. The Consensus recommended citalopram as firs-line treatment for IFN-induced depression. Antidepressant treatment should be continued for at least 12 weeks following the end of IFN treatment. Antidepressant treatment is also indicated for those patients with baseline depressive symptoms and for those with history of IFN-induced depression. Treatment with antidepressants is generally not recommended for all HCV patients and should be used on an individual basis (
41). Not only IFN itself is associated with depression, but it seems that HCV might also be associated with mood problems. Again, a part of this link can be explained by HCV-accompanied factors (such as personality problems, high-risk behavior, stigma, and substance abuse). However, there is evidence that some specific genotypes of HCV such as 3a might be associated with increased risk of depression (
9,
55). Evidence of HCV neuro invasion may be another explanation for the association between mental disorders and HCV (
9,
55).Anxiety disorders in patients with HCV seem to parallel depressive disorders in prevalence rates. Using Structured Clinical Interview for DSM-IV Axis I (SCID-I) in a sample of 500 patients with HCV, prevalence of any depressive disorder, MDD, generalized anxiety disorders, and panic disorders were 18.2%, 6.4%, 7.0% and 5.8% respectively (
56).