The questions below come up most often with prospective users, prescribers, and reviewers. Every answer is informational only — StackRx flags and predicts; it does not prescribe. Not a substitute for medical advice.
The overstacking engine runs four detectors on every stack change. (1) Pairwise drug-drug interactions, drawn from FDA drug labeling and a maintained interaction table that covers ARV/PrEP-specific pairs (tenofovir with nephrotoxic agents, St John's Wort with antiretrovirals, rifampin with antiretrovirals, boosted protease inhibitors with simvastatin or lovastatin, Biktarvy with dofetilide or dronedarone, dolutegravir with mineral antacids). (2) Therapeutic duplication, flagging two or more medications that resolve to the same therapeutic class. (3) Lab contraindications, comparing each medication against documented thresholds (tenofovir with low eGFR ≤60 is critical, metformin at reduced eGFR thresholds, statins with elevated ALT, ACE-i or ARB with hyperkalemia, valproate with transaminitis). (4) Dosing anomalies, comparing each dose against a per-medication standard maximum — doses above the maximum raise a caution flag, doses at 1.5× or more the maximum raise a critical flag; injectable and as-needed medications are skipped because they have no daily total to compare. Each engine finding carries a "discuss with your prescriber" disclaimer in its message field, and the response object includes a top-level disclaimer line. Not a substitute for medical advice.
Anticholinergic burden is a cumulative measure of medications with anticholinergic activity taken together, scored on the Anticholinergic Cognitive Burden (ACB) scale. Each anticholinergic medication in the stack gets a per-medication ACB score from 0 (none) to 3 (definite anticholinergic activity), then the engine surfaces the cumulative burden across the full stack. A single medication is rarely the problem, but two ACB-3 medications is a documented cognitive-risk signal — the engine flags it as informational. The engine also flags overlap with the 2023 AGS Beers Criteria medications to use with caution in older adults, and cross-class combinations (antihistamines plus tricyclic antidepressants plus bladder antispasmodics) that stack additively even when prescribed by different specialists. The ACB scale is the gold standard referenced in geriatric guidelines worldwide. Not a substitute for medical advice.
Compound accumulation tags every medication and supplement by metabolic pathway, hepatic load, and active-ingredient redundancy, then surfaces when the stack is doubling up on the same signals. Specifically: (1) pathway overlap — multiple medications or supplements hitting the same metabolic pathway (CYP3A4, CYP2D6, and others), even across prescribers; (2) active-ingredient duplication — two products containing the same active molecule, such as two magnesium supplements or two fish-oil products with overlapping EPA/DHA; (3) hepatic load — cumulative load on liver metabolism, with NIH LiverTox-documented hepatotoxic agents flagged at elevated ALT; (4) herb-drug interactions at the documented mechanism level — St John's Wort, grapefruit, kava, comfrey, and others. Pathway tagging uses NIH Office of Dietary Supplements ingredient data with cross-references to LiverTox and NCCIH herb-drug guidance. Not a substitute for medical advice.
The printable doctor handoff PDF exports your self-entered medication stack, your key lab markers, and the citation-backed flags the detection engines fired on — into a single briefing a prescriber can review in one sitting. It includes each medication by name and dose, the lab values that informed the engine output, the specific signals each engine raised (for example "tenofovir × low eGFR 52"), the primary-source citation each signal traces back to, and a closing disclaimer line. The brief is designed for the prescriber — primary care, specialist, pharmacist — who is reviewing your stack and wants a one-page summary of what the engines flagged and why. StackRx does not transmit the brief to your prescriber for you; you bring it to the visit. Not a substitute for medical advice.
Because recommending a dose change, a substitution, or a new medication is prescribing — and a product cannot prescribe without a license, without seeing the patient, and without the clinical context a prescriber is trained to weigh. StackRx operates as an information product: it reads your self-reported inputs, points at what primary literature says about them, and surfaces the signals. Decisions about what to take, how much, and when are decisions that belong to you and your prescriber, made in the visit. The Posture page states this in the same language the product itself operates under. Not a substitute for medical advice.
See the Posture page for the full liability statement.
StackRx sends a monthly email reminder so you can re-enter your stack and refresh the engine output. Meds change, doses change, and labs move — the engines reflect what you have reported, so a re-scan keeps the signal current. The reminder is opt-out: notification preferences live in account settings, and turning the re-scan reminder off stops future sends without affecting the rest of the product. Treating the stack as a snapshot rather than a permanent record is part of how StackRx operates as information, not advice. Not a substitute for medical advice.
Enter your medication list and lab markers. The free tier covers up to four medications with full engine output and a printable doctor brief.
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