What urine amphetamine concentration range can be expected after a healthy adult takes 20 mg of immediate‑release Adderall (mixed amphetamine salts) daily?

Expected Urine Amphetamine Levels with 20mg Adderall IR Daily

After taking 20mg of immediate-release Adderall daily, expect peak urine amphetamine concentrations ranging from approximately 2,645 to 5,948 ng/mL, with levels remaining above the standard 500 ng/mL cutoff for up to 47.5 hours post-dose. 1

Peak Concentration Range

• Peak urinary amphetamine concentrations following a single 20mg Adderall IR dose range from 2,645 to 5,948 ng/mL across healthy individuals. 1
• The timing to reach peak concentration is highly variable, occurring anywhere from 2 to 18 hours after administration. 2
• With daily dosing, steady-state levels will be achieved, potentially resulting in consistently elevated baseline concentrations between doses. 1

Detection Window and Cutoff Considerations

• Urine samples containing ≥500 ng/mL amphetamine (the standard GC-MS administrative cutoff) can be detected for up to 47.5 hours after a single 20mg dose. 1
• The number of individual urine voids containing ≥500 ng/mL ranges from 7 to 13 samples per person over the detection period, reflecting significant inter-individual variability. 1
• At the higher 1,000 ng/mL cutoff commonly used in workplace drug testing, 88% of urine specimens test positive following a 20mg dose. 2

Enantiomer Composition (Distinguishing Feature)

• Adderall produces a unique 3:1 ratio of d-amphetamine to l-amphetamine in urine, which distinguishes it from pure d-amphetamine formulations (like Dexedrine) or most illicit amphetamine. 1
• The proportion of l-enantiomer increases over time as the enantiomers are metabolized at different rates, providing a temporal marker for time since last dose. 1, 3
• This enantiomeric profile is critical for medical review officers to differentiate legitimate Adderall use from illicit amphetamine abuse. 1

Factors Affecting Concentration Variability

• Drug concentration profiles show substantial within-subject and between-subject variability due to urine dilution and pH fluctuations. 1
• Amphetamine excretion increases with increasing urine flow (more dilute urine paradoxically shows higher excretion rates) and decreasing urine pH (more acidic urine). 2
• Approximately 35-44% of the administered amphetamine dose is excreted unchanged in urine over 24 hours. 2

Immunoassay Testing Considerations

• Not all urine samples containing ≥500 ng/mL total amphetamine will test positive on immunoassay screening due to the presence of the l-enantiomer, which has lower cross-reactivity. 1
• The optimal cutoff concentration for amphetamine screening should be 500 ng/mL or higher to avoid excessive false-positive results from cross-reactive substances; cutoffs below 500 ng/mL result in only 86% specificity. 4
• At 500 ng/mL cutoff, specificity increases to 99% while maintaining 91% sensitivity. 4

Clinical Interpretation Pitfalls

• A positive urine amphetamine test only confirms amphetamine exposure at some point prior to specimen collection—it does not indicate timing, dose, or impairment. 2
• The wide overlap in amphetamine concentrations following different doses (peak levels of 620-3,160 ng/mL after just 5mg) makes it impossible to back-calculate the administered dose from urine concentration alone. 2
• High concentrations of cross-reactive sympathomimetic amines (like pseudoephedrine) may mask low concentrations of actual amphetamine in immunoassay testing. 5