Purpose: The newly developed “Herlev Hospital Empowerment of Relatives through More and Earlier information Supply” (HERMES) intervention systematically identifies cancer caregivers’ unmet needs for information from health care professionals (HCPs) and offers them the information they lack. The aim of this study was to investigate the effect of the HERMES intervention on caregivers’ perception of information, communication, attention and help from HCPs, fulfillment of care needs, and anxiety and depression. Methods: A randomized intervention study with immediate intervention in the intervention group and delayed intervention (after follow-up) in the control group among caregivers of cancer patients starting chemotherapy. Results: Totally 199 caregivers were included (intervention group, n = 101; control group, n = 98). No intervention effect was found on overall satisfaction with information from HCPs (p = 0.1687) measured by a single item from the Cancer Caregiving Tasks, Consequences and Needs Questionnaire (CaTCoN) and chosen as primary outcome. However, positive effects were found on the CaTCoN subscales “Problems with the quality of information from and communication with HCPs” (p = 0.0279), “Lack of information from HCPs (HERMES)” (p = 0.0039), and “Lack of attention on the caregivers’ wellbeing from HCPs” (p < 0.0001). No effect was found on the CaTCoN subscale “Need for help from HCPs”, the Family Inventory of Needs subscale regarding fulfillment of care needs, or the Hospital Anxiety and Depression scale. Conclusions: Although no effect was found on overall satisfaction with information, the HERMES intervention had positive effects on the caregivers’ experiences of the amount of information and attention given to them and the quality of information and communication. Trial registration: ClinicalTrials.gov (Identifier: NCT02380469).