Joint Task Force to Combat Opioid Trafficking Act of 2018 This bill amends the Homeland Security Act of 2002 to authorize the Department of Homeland Security (DHS) to establish a joint task force to enhance DHS border security operations to detect, interdict, and prevent narcotics, such as fentanyl and other synthetic opioids, from entering the United States. The task force may coordinate with the private sector and with other federal, state, local, tribal, territorial, or international task forces and entities. DHS shall determine whether to establish the task force and notify Congress of its determination within 90 days.