There is an urgent need for the development of effective pain medication that is also safe. Current pain medications targeting the mu-opioid receptor such as morphine, fentanyl and tramadol are addictive, and are ineffective when used long term. Use of these pain medications contributes to the opioid crisis, which kills hundreds of people each day. In New Zealand, 1 in 5 adults suffer from chronic pain and 50% of pain sufferers report little pain relief with current treatments. This causes significant impact on the health and wellbeing of pain and addiction sufferers, their whānau and society. Our novel drugs targeting the kappa-opioid system are not addictive and do not cause fatal respiratory side-effects. This study will use our novel drug library to select the best compound that is effective in treating pain and devoid of side-effects to progress to clinical use.