Plasma Levels of Methylphenidate Track Clinical Response in Youth with ADHD Better Than Urine Tests

The study, published in Child and Adolescent Psychiatry and Mental Health, analyzed hundreds of biological samples from young patients receiving methylphenidate treatment and connected the measured drug levels to same-day assessments of symptoms, behavior, and neuropsychological function.

Therapeutic drug monitoring, or TDM, is the practice of measuring drug concentrations in a patient’s body to guide dosing. In principle, it can improve treatment efficacy and reduce adverse effects, but for methylphenidate in youth with ADHD, data on drug concentration patterns according to sampling time and the clinical significance of monitoring drug levels have remained limited. The new study set out to address that gap by collecting both urine and plasma samples from the same patients and examining how the concentrations related to clinical outcomes.

The research team gathered a total of 355 urine samples and 236 plasma samples from 311 ADHD patients receiving methylphenidate. Levels of methylphenidate and its main metabolite, ritalinic acid, were determined using ultra-performance liquid chromatography-tandem mass spectrometry, a highly sensitive laboratory technique capable of quantifying small molecules at very low concentrations. Importantly, comprehensive assessments of ADHD symptoms were conducted on the same day, immediately after urine or blood sample collection, allowing the researchers to link each measured concentration directly to that patient’s current clinical state.

The analysis revealed striking differences in concentration between the parent drug and its metabolite. The median urinary concentration of methylphenidate was 346.6 micrograms per milliliter, with an interquartile range of 89.05 to 893.8, while the median urinary concentration of ritalinic acid was far higher at 19,968.8 micrograms per milliliter, with an interquartile range of 5,898.9 to 53,311.3. The study also identified more than four hours after dosing as the optimal urine collection interval for monitoring purposes.

In plasma, the picture was different. The median plasma concentration of methylphenidate was 8.15 nanograms per milliliter, with an interquartile range of 4.68 to 11.95, and the median plasma concentration of ritalinic acid was 201.85 nanograms per milliliter, with an interquartile range of 111.28 to 304.6. These figures illustrate how the drug and its metabolite distribute very differently across biological matrices, which matters for any laboratory attempting to interpret a single measurement in a clinical setting.

When the researchers compared plasma and urinary analyte levels, they observed weak-to-moderate correlations. Plasma methylphenidate correlated with its urinary counterpart at r = 0.297, and plasma methylphenidate correlated with urinary ritalinic acid at r = 0.280, both statistically significant at p < 0.001. The modest strength of these correlations indicates that a urine measurement does not reliably substitute for a plasma measurement, since each matrix reflects the drug’s behavior differently.

The most consequential finding concerned clinical relevance. Plasma-based therapeutic drug monitoring demonstrated greater clinical relevance than urine-based monitoring, showing significant associations with manifestations of target response, variability in response consistency, the ability to shift between tasks, and inconsistency in reaction times over longer intervals. In other words, the concentration of methylphenidate in plasma was the measurement that tracked how consistently patients responded to the medication and how their cognitive performance varied, dimensions that are central to evaluating whether an individual’s treatment is working well.

The authors conclude that the study provides new insights into therapeutic drug monitoring in ADHD patients for optimizing therapeutic strategies, and they position the work as a foundation for future longitudinal studies. Because the reported findings come from a cross-sectional sample collection design, with assessments taken on a single day for each patient, the associations described here do not by themselves establish how changing drug levels over time would alter treatment outcomes. The article was published as an open-access accepted manuscript on 1 October 2026, subject to further editorial edits before the final version of record. Even so, the work offers clinicians and researchers a detailed reference point for the concentrations of methylphenidate and ritalinic acid expected in both plasma and urine, and a data-driven argument that plasma-based monitoring deserves priority in future efforts to personalize methylphenidate dosing for young patients with ADHD.

Subject of Research: Therapeutic drug monitoring of methylphenidate in youth with attention-deficit/hyperactivity disorder

Article Title: Optimizing methylphenidate treatment in attention-deficit/hyperactivity disorder: clinical utility of therapeutic drug monitoring and comprehensive outcomes in youth

Article References: Huang, W.-T., Chen, C.-M., Lee, S.-Y., Li, C.-J., Tsai, C.-S., Chou, W.-J., You, H.-L., & Wang, L.-J. (2026). Optimizing methylphenidate treatment in attention-deficit/hyperactivity disorder: clinical utility of therapeutic drug monitoring and comprehensive outcomes in youth. Child and Adolescent Psychiatry and Mental Health. https://doi.org/10.1186/s13034-026-01182-6

Image Credits: AI Generated

DOI: 10.1186/s13034-026-01182-6

Keywords: ADHD, methylphenidate, therapeutic drug monitoring, children and adolescents, pharmacokinetics, ritalinic acid, plasma concentration, urine testing, neuropsychological function, UPLC-MS/MS, Optimizing, treatment