Drug detection time is the maximum time you can find traces of substances and their metabolites by chemical tests of urine, hair, saliva and blood. It is rare to prove a substance use after detection time.

Maximum detection time can vary in a range from hours to months, depending on test performed, duration of abuse, individual factors and health conditions.

False-positive results may depend on substances found in foods or prescription drugs.

Most drugs will generally appear in your urine or saliva within 2 – 8 hours after use. Blood tests allow an almost immediate detection. Drugs can be detected in your hair about 5 – 7 days after use. Detection in hairs depends on hairs growth and it covers longer periods.

Laboratory tests seek substances and their metabolites (molecules derived by the transformation of the substance in the body). Metabolites are stored in fast growing tissues (hair, nails) and in fat tissue. Fat people have a greater accumulation of metabolites.
Detection time of a substance may vary by:
Quantity and frequency of use: Single use or small doses are less detectable than a long-term chronic use.

Speed of Metabolization: Individual features based on genetics.

Mass: In general, metabolic activity slows down in overweight people

Physical Activity: Sedentary habits involve a greater percentage of fat mass and a slower metabolic activity. Physical activity aids to eliminate metabolites more rapidly.

Age: Usually metabolism speed slows down with age.

Health status: Poor health condition, as it often appears in chronic drug users, slow down the metabolism.

Tolerance: Chronic users develop tolerance, meaning faster substances metabolism.

Urine PH: when urine is acid, generally it takes shorter time to clear substances.

Hair or body hairs test: A sample of hairs can be taken from any part of the body. To hide substances use, shaving is useless: 3 cm length reports the history of the last 90 days of use. Hair can keep traces of substances even for months.

Blood test.  Notes on the drug detection time for blood drug test: blood test can verify acute intoxication and can be conducted together with urine test. Drugs are generally detectable in blood within 2 days, excepted cannabis and tobacco derivatives (THC and nicotine) eliminated in a longer time.