Adderall/Stimulant Decay Calculator

Pharmacokinetics: Understanding How Drugs Leave the Body

When you take a medication like Adderall (mixed amphetamine salts), it doesn't just disappear instantly. It follows a mathematical decay curve known as "half-life elimination." Our Adderall Decay Calculator helps patients and medical students visualize this process, estimating how much active substance remains in the bloodstream over time.

What is Half-Life?

The biological half-life is the time it takes for the concentration of a drug in your body to reduce by exactly 50%.
For Adderall:
- d-Amphetamine: Half-life is roughly 10 hours.
- l-Amphetamine: Half-life is roughly 11-13 hours.
For simplicity, we often use an average of **10-12 hours** for calculation purposes, though individual metabolism varies widely based on liver function, pH levels, and genetics.

The Elimination Formula

The amount of drug remaining ($N_t$) at time $t$ can be calculated using the exponential decay formula:

$$N(t) = N_0 \times (0.5)^{\frac{t}{T_{1/2}}}$$

Where:
- $N_0$ = Initial dose (mg)
- $t$ = Time elapsed (hours)
- $T_{1/2}$ = Half-life of the drug (hours)

Example: You take 20mg at 8:00 AM.
By 6:00 PM (10 hours later), 10mg remains (50%).
By 4:00 AM the next day (20 hours total), 5mg remains (25%).
By 2:00 PM the next day (30 hours total), 2.5mg remains (12.5%).

Drug Testing Windows

It is important to note that "active therapeutic effect" is different from "detectable metabolites."
While the effect of the medication typically wears off in 4-6 hours (Immediate Release) or 10-12 hours (Extended Release), the metabolites can be detected in:
- **Urine:** 2 to 4 days.
- **Hair:** Up to 90 days.
- **Saliva:** 24 to 48 hours.
Factors like urinary pH significantly affect excretion. Acidic urine clears amphetamines faster, while alkaline urine keeps them in the system longer.

Disclaimer

This calculator is for educational purposes only. It uses average statistical models and cannot predict exact drug levels for any specific individual. Never adjust your dosage without consulting your prescribing physician.