Many opponents believe that replacement drugs only substitute one addiction with another, and that methadone can be manipulated and exploited in some cases. Long-term usage has the ability to cause brain changes. Methadone causes changes in thought, cognitive performance, and memory by influencing nerve cells in the brain. An initial review is performed during alcohol therapy. The person will be evaluated and interviewed during this evaluation, and then the treatment team will then devise the optimal treatment plan for that individual. Methadone 
Methadone is a drug used for both opioid overuse treatment and for chronic pain, it is known as a full opioid agonist. Methadone is the most common prescribed out of all the medications used for addiction; this is due to the fact that it has more advantages and less disadvantages than the other medications. Due to methadones longer half life, it is much more challenging to prescribe dosage amounts compared to others. The long half life has good benefits, one of these benefits being the fact that if a dose is missed in the 24 hours of the last, the patient will not typically struggle with withdrawal symptoms quite yet. Methadone can be found in a couple different forms: tablet, oral solution, or an injection. The first time this medication was put to use was during World War II, it was a safer alternative to morphine. Buprenorphine
Buprenorphine is a partial opioid receptor agonist. Unlike methadone and other full opioid receptor agonists, buprenorphine is less likely to cause respiratory depression due to its ceiling effect.
This points to a potential for greater addictive capacity in these individuals who require higher dosages to achieve pain control. However, evidence linking the 118A>G variant to opioid dependence is mixed, with associations shown in a number of study groups, but negative results in other groups. One explanation for the mixed results is the possibility of other variants which are in linkage disequilibrium with the 118A>G variant and thus contribute to different haplotype patterns that more specifically associated with opioid dependence. Non-opioid receptor genes
The preproenkephalin gene, PENK, encodes for the endogenous opiates that modulate pain perception, and are implicated in reward and addiction. (CA) repeats in the 3 flanking sequence of the PENK gene was associated with greater likelihood of opiate dependence in repeated studies. Variability in the MCR2 gene, encoding melanocortin receptor type 2 has been associated with both protective effects and increased susceptibility to heroin addiction. The CYP2B6 gene of the cytochrome P450 family also mediates breakdown of opioids and thus may play a role in dependence and overdose. Diagnosis
The DSM-5 guidelines for the diagnosis of opioid use disorder require that the individual has a significant impairment or distress related to opioid uses.