Methadone is a synthetic opioid analgesic renowned for its dual action as a full agonist at the mu-opioid receptor and antagonist at the NMDA receptor, distinguishing it from traditional opioids like morphine. It acts centrally on the CNS, modulating k- and o- opioid receptors alongside serotonin and norepinephrine uptake. This mechanism underlies its effectiveness in managing chronic pain and opioid use disorder (OUD).

Administered orally, Methadone exhibits onset within 30 minutes and peaks after approximately 3 hours, with a prolonged half-life ranging from 15 to 24 hours with repeated doses. It's available in various forms—oral tablets (5 mg, 10 mg), dispersible tablets (40 mg), oral solutions (5 mg/5 ml, 10 mg/5 ml), injectable solutions (10 mg/ml), and oral concentrate solutions (10 mg/ml).

In clinical practice, Methadone is pivotal for chronic pain management due to its sustained efficacy and reduced neurotoxic and constipative side effects compared to other opioids. It also plays a critical role in MAT for OUD, helping individuals alleviate cravings and withdrawal symptoms, thereby facilitating recovery from heroin and other opioid dependencies.

Overall, Methadone's unique pharmacological profile and diverse formulations make it a cornerstone in treating both chronic pain and OUD, offering patients effective relief while minimizing adverse effects associated with traditional opioid therapies.