Biphalin TFA, a BBB-penetrable opioid peptide analog, contains two active enkephalin pharmacophores. Biphalin TFA has high affinity for opioid receptors. Biphalin TFA shows analgesic effect in acute, neuropathic, and chronic animal pain models. Biphalin TFA is also an antiviral , antiproliferative, anti-inflammatory, and neuroprotective agent.