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The elimination half-life of methadone ranges from 8 to 59 hours. In particular, the (R, S)-methadone half-life can be around 15 to 60 hours. For (R)-methadone, it is around 10 to 40 hours. Its analgesic action, on the other hand, can range from 4 to 8 hours. Despite the medication’s ability to reach its peak concentration within 4 hours in blood plasma, methadone can be traced in the bloodstream half an hour after an oral ingestion or intravenous administration.

  • Methadone can be acquired as an oral solution or in a powder, tablet or liquid concentrate form.
  • Generally, methadone is administered orally.
  • Other unconventional ways of administration include injecting and snorting, which are often indicators of abuse or misuse.
  • The DEA categorized methadone under Schedule II narcotics, which means that it can be used for medical purposes.
  • Methadone is high risk for abuse, dependence, and addiction.

Various factors can influence the length of stay of methadone in the system.


Generally, elderly patients over 65 years old metabolize the drug at a slower rate and excrete it from their system longer. These processes take a longer time to complete because of existing problems in the kidney or liver, decreased hepatic blood flow, and slower metabolism among others.

Body height, weight, and fat accumulation

The greater dose of medication you ingest in contrast to your body mass, the more time it will take for the medication to be excreted from your body, and vice-versa. Take note that this lipid-soluble substance can accumulate in the body fat. Hence, those with an overall lesser body fat cannot accumulate as much of the drug. Therefore, the excretion of the medication from the system happens faster.


Another factor that contributes to a faster elimination of methadone from the body can be genes. The genetic print has predetermined rapid metabolizers contrary to the so-called poor metabolizers.


More research is needed to know whether an empty stomach or the presence of food in the body can impact the absorption rate of methadone as well as how it is metabolized and excreted from the body. Studies suggest that a diet rich in high-fat food can possibly enhance methadone absorption and also increase the bioavailability of the drug.

Liver function

The liver carries the burden of metabolizing methadone through various CYP450 enzymes. However, this is more notable by the CYP3A4 enzyme. Those diagnosed with hepatic impairment are often unable to quickly metabolize methadone compared to people with normal liver functions.

Urinary pH

A urinary pH that leans more on the acidic environment can speed up the elimination of methadone from your system. On the other hand, a very alkaline urine is more likely to execute drug reabsorption than drug elimination, which can extend the time frame by which the drug clears out from your body.

Frequency of use

If you have been using methadone for a long time already, chances are the drug has accumulated in your body in excessive amounts. When this is the case, drug elimination may also be prolonged.


If you have dosed on methadone in large quantities each intake, slower drug elimination is more likely.

Other medications

Medications known to inhibit the CYP3A4 enzyme have the tendency to interact with the metabolism of the drug; often resulting in a longer clearance time. These medications include Ritonavir, Clarithromycin, Indinavir, Nefazodone, and Ketoconazole. Meanwhile, drugs like Phenobarbital, Carbamazepine, St. John’s wort, Modafinil, Glucocorticoids, and Rifampicin are known to activate the CYP3A4 enzyme resulting in a shorter clearance time.

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