What is the full μ-receptor agonist used primarily in federally regulated opioid treatment programs?

Methadone is a full μ-receptor agonist that is primarily utilized in federally regulated opioid treatment programs. It is effective in managing opioid dependence due to its ability to activate the μ-opioid receptors in the brain, thereby providing pain relief and reducing withdrawal symptoms. Methadone's long half-life allows for stable dosing, which can prevent the highs and lows associated with shorter-acting opioids, making it an ideal choice for maintenance therapy in patients with opioid use disorders.

In contrast, the other options serve different functions. Buprenorphine is a partial agonist at the μ-receptor and has a ceiling effect that reduces the risk of overdose. Naltrexone, on the other hand, is an opioid antagonist, which blocks the effects of opioids and is used for treating opioid use disorder but is not an agonist. Topiramate is an anticonvulsant and does not specifically act on opioid receptors, making it unrelated to the treatment of opioid dependence.

Therefore, Methadone stands out as the correct answer for its critical role in opioid treatment programs due to its full agonist action, which provides necessary support for individuals in recovery from opioid addiction.