Methadone has a slow metabolism and very high fat
solubility, making it longer lasting than morphine-based drugs. Methadone has a typical elimination half-life of 15 to 60 hours with an average of i would say about 22. However, metabolism rates vary greatly between individuals, up to a factor of 100 ranging from as few as 4 hours to as many as 130 hours, or even 190 hours. So it's hard to say.