Melatonin 3mg and 5mg Compared to Cognitive Behavioral Therapy for Insomnia (CBT-I) in the Treatment of Insomnia

Inclusion Criteria: * Fulfill the criteria for insomnia disorder, according to DSM-5 (Diagnostic and Statistical Manual of Mental Disorders, 5th Edition); * Complaint of difficulty falling asleep; * Ability to understand and consent their participation in this clinical study, expressed by signing the Informed Consent Form (ICF). Exclusion Criteria: * Any finding of clinical/physical observation or laboratory examination to be interpreted by the investigator as a risk to the inclusion of the participant in the clinical study; * Known hypersensitivity to drug components used during the study; * Participant have any family relationship to the second degree or bond with employees or employees of Sponsor and Sites; * Participant has used beta-blockers (in the last 30 days prior to screening visit), psychoactive drugs or sedative effect, such as, but not limited to: sedatives (in the last 14 days prior to screening visit), hypnotics (in the last 07 days prior to screening visit), muscle relaxants (in the last 11 days prior to screening visit), antihistamines first generation (in the last 08 days prior to screening visit), and antidepressants, antiepileptics, antipsychotics, among others (in the last 30 days prior to screening visit); * Participants diagnosed with clinical diseases that interfere with sleep, such as chronic pain, nocturia, hypothyroidism, hyperthyroidism, severe heart disease, serious neurological and psychiatric disorders according to the assessment of the investigator; * Participants diabetics insulin dependent; * Sleep apnea moderate to severe - AHI \> 20 (Apnoea-Hypopnoea Index) assessed by polysomnography at the baseline; * Participants who work at night; * Participant who has BMI ≥ 30; * Participant score above 50 in Anxiety Inventory to assess the degree of anxiety; * Participant with cognitive impairment, based on the result obtained in the Mini-Mental State Examination. The cognitive impairment will be considered with score below 13 points for illiterates, below 18 for participants with one to eight incomplete years of schooling, below 26 for those with education of eight or more years; * Participant score above 20 on the Beck Inventory to assess depression; * Abuse of alcohol or illicit drugs, according to the assessment of the investigator; * Male participants who do not agree to use acceptable methods of contraception; 1) male participants: barrier methods, except surgically sterile (vasectomy) or participants who declare to perform sexual practices on a not to reproductive way. 2) methods of contraception for the male participant's partner: oral contraceptives, injectable contraceptives, intrauterine device (IUD), hormonal implants, hormonal patch, tubal ligation and barrier methods; except surgically sterile (bilateral oophorectomy or hysterectomy) or the menopausal for at least one year; * Female participants who are in the reproductive age and do not agree to use acceptable methods of contraception (oral contraceptives, injectable contraceptives, intrauterine device (IUD), hormonal implants, barrier methods, hormonal patch and tubal ligation); except surgically sterile (bilateral oophorectomy or hysterectomy), the menopausal for at least one year and participants who declare to perform sexual practices on a not to reproductive way; * Women in gestation period or who are breastfeeding; * Participant who has participated in clinical trial protocols in the last twelve (12) months (CNS Resolution 251 of August 7, 1997, Part III, sub-item J), unless the investigator considers that there may be a direct benefit to the same.