Adderall is primarily broken down in the liver, with a significant portion also excreted unchanged through the kidneys. About 35% to 44% of a dose leaves the body as unmetabolized amphetamine in urine within 24 hours, meaning your liver only needs to process roughly half to two-thirds of each dose. The speed of that clearance depends on your genetics, your urine pH, and which of Adderall’s two active components you’re looking at.
The Two Isomers Clear at Different Speeds
Adderall contains two forms of amphetamine: d-amphetamine (dextroamphetamine) and l-amphetamine (levoamphetamine). These are mirror-image molecules with different potencies and different clearance times. In adults, d-amphetamine has a mean elimination half-life of 10 hours, while l-amphetamine lingers longer at about 13 hours. That three-hour gap means l-amphetamine builds to slightly higher concentrations with repeated dosing and takes longer to fully leave your system.
In children aged 6 to 12, both isomers clear faster: roughly 9 hours for d-amphetamine and 11 hours for l-amphetamine. Adolescents fall in between, with half-lives of about 11 hours and 13 to 14 hours, respectively. These age differences reflect the fact that children generally have faster metabolic rates relative to their body size.
What Happens in the Liver
The liver enzyme CYP2D6 plays a central role in amphetamine metabolism. This enzyme processes the amphetamine molecule in several ways: it can attach a chemical group to the ring structure of the molecule (producing an active metabolite called 4-hydroxyamphetamine), or it can modify the side chain to produce norephedrine, another active compound. Both of those metabolites are then further converted into 4-hydroxy-norephedrine.
A separate pathway breaks down the side chain through a process called deamination, ultimately producing benzoic acid and hippuric acid, which are inactive waste products your kidneys easily flush out. The key point is that some of the intermediate metabolites are pharmacologically active, meaning they still have stimulant effects before being broken down further. This is one reason Adderall’s effects can persist even as the parent drug is being cleared.
Your Genetics Change How Fast It Works
CYP2D6 is one of the most genetically variable enzymes in the human body, with over 70 known gene variants. These variants sort people into four broad categories: poor metabolizers (who essentially lack functional copies of the gene), intermediate metabolizers, extensive (normal) metabolizers, and ultra-rapid metabolizers (who carry extra copies of functional genes and produce more of the enzyme).
Poor metabolizers process amphetamine through the CYP2D6 pathway much less efficiently. Research on closely related stimulants shows that poor metabolizers can experience heightened drug effects even when their blood levels of the drug look similar to those of normal metabolizers. The leading explanation is that brain concentrations end up higher in poor metabolizers, or that their nervous system responds more steeply to whatever concentration is present. If you’ve ever felt that a standard dose hits you unusually hard, or barely works at all, CYP2D6 genetics may be part of the reason.
On the other end, ultra-rapid metabolizers break the drug down faster, which can make a dose feel weaker or shorter-lasting. Interestingly, faster metabolism through CYP2D6 also generates more of the active and potentially neurotoxic intermediate metabolites, which is a tradeoff that researchers are still working to quantify in clinical terms.
Urine pH Has a Dramatic Effect
Amphetamine is a weak base, and its clearance through the kidneys is heavily influenced by how acidic or alkaline your urine is. The mechanism is straightforward: in acidic urine, amphetamine molecules become electrically charged (ionized), which prevents them from being reabsorbed back into the bloodstream through the kidney tubules. They stay in the urine and get flushed out. In alkaline urine, more of the drug stays in its uncharged form, passes back through the kidney walls, and recirculates in the blood.
The magnitude of this effect is striking. When urine shifts from alkaline (pH around 7.5 to 8.5) to acidic (pH around 4.5 to 5.5), the amount of amphetamine excreted unchanged in urine can increase up to 11-fold. Going the other direction, alkaline urine can roughly double the total drug exposure in plasma compared to normal, uncontrolled urine pH. This is why the FDA label for Adderall notes that acidifying agents like vitamin C (ascorbic acid) and glutamic acid can lower blood levels of the drug, while alkalinizing agents can raise them.
In practical terms, this means that drinking large amounts of orange juice or taking vitamin C supplements around the time of your dose could reduce how well it works. Conversely, a diet high in alkaline-promoting foods or use of antacids like sodium bicarbonate could intensify and prolong its effects. The timing matters most within a few hours of taking the medication.
The Pathway Doesn’t Get Overwhelmed
One notable feature of amphetamine metabolism is that it follows first-order kinetics across a very wide dose range. In plain terms, this means your body clears a consistent percentage of the drug per hour regardless of how much is in your system. Research has demonstrated that even at doses as high as 500 mg (far beyond any therapeutic dose, which typically ranges from 5 to 30 mg), the metabolic and excretion pathways do not become saturated. The kidney’s active transport system for excreting amphetamine also stays well below its maximum capacity at these concentrations.
This is relevant because some drugs become dangerous partly because the liver can’t keep up at higher doses, causing blood levels to spike disproportionately. Amphetamine doesn’t behave this way. Toxicity from high doses is driven by the drug’s direct effects on the brain and cardiovascular system, not by a metabolic bottleneck.
How Long Until It’s Fully Gone
A rule of thumb in pharmacology is that a drug is essentially cleared after five half-lives. For d-amphetamine in adults, that works out to roughly 50 hours (just over two days). For l-amphetamine, it’s closer to 65 hours (about 2.5 to 3 days). Standard urine drug tests can typically detect amphetamine for one to three days after the last dose, though this window stretches or shrinks depending on urine pH, individual metabolism, and how long you’ve been taking the medication.
Because a large fraction of each dose (35% to 44%) passes through the kidneys unchanged, anything that affects kidney function or urine chemistry has a proportionally large impact on total clearance. The liver handles the rest, producing a mix of active and inactive metabolites that are themselves excreted in urine. The combination of these two routes, renal excretion and hepatic metabolism, is why both your genetic enzyme profile and your diet can meaningfully shift how long Adderall stays active in your body.