when initiating buprenorphine/naloxone include withdrawal symptom severity, the time since last opioid use, and the type of opioid used (long-acting vs. short-acting). Though not standard practice, clinicians are exploring micro-induction protocols for buprenorphine/naloxone that prioritizes rapid induction with small, increasing doses. The theoretical benefit of this form of induction is that treatment can be initiated irrespective of withdrawal symptoms.Some formulations of buprenorphine incorporate the opiate antagonist naloxone during the production of the pill form to prevent people from crushing the tablets and injecting them, instead of using the sublingual (under the tongue) route of administration. Buprenorphine/naloxone formulations are available as tablets and films. The combined tablet works via sublingual administration because buprenorphine maintains adequate bioavailability (35-55%) while naloxone doesn't (~10%). When injected, naloxone has higher bioavailability, thereby blocking the pain and craving-reducing effects of buprenorphine. Naltrexone Naltrexone is an opioid receptor antagonist used for the treatment of opioid addiction. Naltrexone is not as widely used as buprenorphine or methadone for OUD due to low rates of patient acceptance, non-adherence due to daily dosing, and difficulty achieving abstinence from opioids before beginning treatment. Additionally, dosing naltrexone after recent opioid use could lead to precipitated withdrawal. Conversely, naltrexone antagonism at the opioid receptor can be overcome with higher doses of opioids. Naltrexone monthly IM injections received FDA approval in 2010, for the treatment of opioid dependence in abstinent opioid users. Other opioids Evidence of effects of heroin maintenance compared to methadone are unclear as of 2010. A Cochrane review found some evidence in opioid users who had not improved with other treatments. In Switzerland, Germany, the Netherlands, and the United Kingdom, long-term injecting drug users who do not benefit from methadone and other medication options may be treated with injectable heroin that is administered under the supervision of medical staff. Other countries where it is available include Spain, Denmark, Belgium, Canada, and Luxembourg. Dihydrocodeine in both extended-release and immediate-release form are also sometimes used for maintenance treatment as an alternative to methadone or buprenorphine in some European countries. Dihydrocodeine is an opioid agonist. It may be used as a second line treatment. A 2020 systematic review found low quality evidence that dihydrocodeine may be no more effective than other routinely used medication interventions in reducing illicit opiate use. An extended-release morphine confers a possible reduction of opioid use and with fewer depressive symptoms but overall more adverse effects when compared to other