A lot of this answer will depend upon your liver function and grade of cirrhosis. Is your total, indirect, or direct bilirubin elevated? Do you have an elevated ammonia level? What were the findings of your most recent liver biopsy? (I hope that your Hepatologist performed this) Do you have elevations of AST, ALT, LDH, or Gamma-GT (GGT)? ... or PT and PTT (blood clotting times)?
If the total and indirect bilirubin, and direct bilirubin for that matter, are normal or close to normal, then this is a good reflection of how well your liver is able to "congugate" chemicals so that they can more easily be eliminated via the urine. Other parametres of your blood chemistry should also be able to provide indications of your liver's capacity to metabolise ... such as ammonia level, medication levels, LDH, among others.
If you have no elevations of bilirubin, AST, ALT, GGT, LDH, ammonia etc ... the capability of the liver to metabolically congugate and metabolise medications and recreational drugs that undergo hepatic metabolism must be reasonably intact. Despite "cirrhosis," the liver is incredibly resilient. The elimination half-life of the methamphetamine will be reasonably close to that expected ... cleared from urine detectable levels within 5 days, based on the 5-panel or 10-panel type screens immunoassays. If Mass Spectroscopy (MS) or Thin Layer Gas Chromatography (GC) techniques are used instead, the level of detection is improved by at least 100%, although there are reports of false positive methamphetamine peaks on certain MS/GC because of the presence of pseudoephedrine or ephedrine (cold and flu remedies, decongestants, weight loss pills) and their respective metabolites. Hair follicle testing and hair shaft testing will be positive for much longer periods depending upon amount used, frequency of use, and chronicity of use ... and also the length of the hair.
If you have hepatic impairment of metabolism or congugation, then the elimination half life will be non-linearly extended, but not predictable without knowing all of your labs and the status of the particular cytochrome p-450 enzymatic system used in methamphetamine breakdown, and the other medications present that use the same cytochrome p-450 enzyme(s), act as substrates, inhibitors, down-regulators, up-regulators ... so IF you have hepatic impairment, the confounding parametres become so complex that the elimination half-life cannot be calculated with any certaintly for blood, urine, or saliva.
So, look at your labs. If there are elevations or perturbations in certain blood tests, especially total and indirect bilirubin, ammonia, ALT, AST, GGT, LDH, PT, PTT, low serum sodium, etc ... then it will be impossible for me to give you a correct answer. If your labs are within normal range, then it is indicative of well-preserved function despite the presence of cirrhotic scarring, and I would safely assume clearance of detectable levels within 5 days by immunoassay (the usual 5 to 10-panel assay).
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XXXXX XXXXX, MD