How long does methamphetamine (meth) stay in the system?

Methamphetamine Detection Time in the Body

Methamphetamine typically remains detectable in urine for 2-4 days after use, with the biological half-life reported to be 4-5 hours. 1

Detection Windows by Testing Method

• Urine testing: The primary method for detecting methamphetamine

  • Standard detection window: 2-4 days after use 2
  • For occasional users: Detection possible for up to 5 days using a 1000 ng/mL cutoff, and up to 6 days using a lower 300 ng/mL cutoff 2
  • For frequent or heavy users: May be detectable for up to 7 days, with some cases showing detection up to a week after last use 3

• Metabolism and excretion factors:

  • Approximately 62% of an oral dose is eliminated in urine within the first 24 hours 1
  • About one-third is excreted as intact drug, with the remainder as metabolites 1
  • Mean urinary terminal elimination half-life is approximately 23.6 ± 6.6 hours 4

Factors Affecting Detection Time

• Urine pH: Alkaline urine significantly increases the drug half-life 1
• Dosage: Higher doses lead to longer detection windows 2
• Frequency of use: Regular users will have longer detection times due to accumulation 4
• Individual metabolism: Significant variation exists between individuals in how quickly they metabolize methamphetamine 3
• Testing methodology: Lower cutoff thresholds (300 ng/mL vs 1000 ng/mL) extend detection time by approximately one day 2

Metabolic Pathway

• Methamphetamine is rapidly absorbed from the gastrointestinal tract 1
• Primary metabolism occurs in the liver through:
  • Aromatic hydroxylation
  • N-dealkylation
  • Deamination 1
• Approximately 2% of methamphetamine is metabolized to amphetamine 3
• At least seven different metabolites have been identified in urine 1

Clinical Implications

• Peak urinary concentrations typically occur 3-7 hours after ingestion 5
• The amphetamine/methamphetamine ratio increases over time, from approximately 13% initially to 36% later in the detection window 4
• Individual metabolic variations can significantly impact detection times, with some users testing positive longer than others despite similar dosing 3

Important Considerations

• Methamphetamine may be detectable in urine for up to 7 days after use in some individuals 3
• Slow urinary excretion results in drug accumulation and increases detection time windows 4
• Some prescription and over-the-counter medications can cause false positives or may metabolize to methamphetamine or amphetamine 5