Ketamine may help reduce the pain of opiate withdrawal and/or reverse opiate tolerance.
"In such cases, it might be worth investigating whether ketamine, widely used by anaesthetists to limit opioid tolerance, reduce use of painkillers, and increase the time preceding the first request for painkillers during the postoperative period [9], may be efficient for managing opioid withdrawal. Ketamine has also shown it has a role to play as an anti-hyperalgesic and tolerance-protective drug. It is acknowledged that it is of interest for managing various pain conditions, such as pain connected with opioid tolerance, acute pain or chronic pain [10–12]. Pain physicians use ketamine at sub-anaesthetic doses to treat refractory chronic pain syndromes, especially cancer- and non-cancer-related pain, or pain with a neuropathic component [13–15]. Moreover, recent publications showed that use of alpha2-adrenoreceptor agonists such as clonidine and NMDA antagonists such as ketamine or dextromethorphan could minimize tolerance development during opioid treatment"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5105239/
"In such cases, it might be worth investigating whether ketamine, widely used by anaesthetists to limit opioid tolerance, reduce use of painkillers, and increase the time preceding the first request for painkillers during the postoperative period [9], may be efficient for managing opioid withdrawal. Ketamine has also shown it has a role to play as an anti-hyperalgesic and tolerance-protective drug. It is acknowledged that it is of interest for managing various pain conditions, such as pain connected with opioid tolerance, acute pain or chronic pain [10–12]. Pain physicians use ketamine at sub-anaesthetic doses to treat refractory chronic pain syndromes, especially cancer- and non-cancer-related pain, or pain with a neuropathic component [13–15]. Moreover, recent publications showed that use of alpha2-adrenoreceptor agonists such as clonidine and NMDA antagonists such as ketamine or dextromethorphan could minimize tolerance development during opioid treatment"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5105239/