After taking methamphetamine (meth), its detectable time in urine is affected by a variety of factors, including individual metabolic differences, frequency of use, dose, body mass index (BMI), liver and kidney function, etc. The following is a comprehensive analysis based on medical research： ### 1. **General metabolic time range** -**Single use**: Ordinary urine test (immunoassay) can usually detect methamphetamine and its metabolites (such as amphetamine) within 1-3 days after smoking. After about 72 hours, most single-user urine tests may turn negative. -**Long-term or frequent use**: The metabolic time is significantly extended, and it may take **4-7 days** or even longer to pass the test. Long-term use can cause the drug to accumulate in adipose tissue and be slowly released into the blood. ### 2. **Key influencing factors** -**Metabolic rate**: Differences in the activity of individual liver enzymes (such as CYP2D6) affect the metabolic rate. For example, patients with liver disease may have longer metabolic time. -**Urine pH value**: Acidic urine (pH<5) Excretion may be accelerated, while alkaline urine delays excretion. -**Sensitivity of detection method**: The cut-off value of ordinary reagents is usually 500 ng/mL (initial screening), while the sensitivity of laboratory confirmation (such as GC/MS) is higher (may be as low as 300 ng/mL). ### 3. **Extended risk of special circumstances** -**High-dose or high-purity meth**: May be extended to **5-7 days**. -**Chronic addicts**: The superimposed effect of the metabolic half-life (9-24 hours) may cause the detection window to exceed **1 week**. ### 4. **Misconceptions about "accelerated metabolism”** -**Drinking plenty of water or diuretics**: Urine may be diluted, but the concentration and specific gravity of creatinine will be tested in the laboratory. Abnormal results may lead to re-examination or be deemed invalid. -**Exercise or detoxification products**: There is no clear evidence to support the effectiveness and may cause health risks. ### 5. **Medical and legal advice** -Long-term abuse of methamphetamine may lead to irreversible nerve damage (such as dopaminergic neuron apoptosis), cardiovascular disease and mental disorders (such as amphetamine psychosis). -At the legal level, evading detection may involve more serious consequences. It is recommended to take the initiative to seek professional detoxification help (such as cognitive behavioral therapy, drug-assisted therapy). ### Summary Under the premise of no other health problems, the average metabolic time after a single use is 1-3 days, and long-term use requires at least 7 days or more. However, individual differences are so great that they cannot be accurately calculated by a general formula. The safest thing to do is to completely quit and consult a medical professional.