Methodology

OptiStacker checks 56 supplements against 47 pairwise rules and 108 medication and health-condition rules. Every rule is written by hand from primary sources — mainly the NIH Office of Dietary Supplements fact sheets, NIH NCCIH, and peer-reviewed studies — and every one links to its sources. Data last reviewed 2026-09-29.

Evidence levels

  • Strong evidenceRandomized trials or authoritative reviews (e.g. NIH ODS).
  • Human dataHuman pharmacokinetic, cohort or case-series data.
  • Mechanism-basedPlausible biological mechanism with little direct human outcome data.
  • Animal / lab onlyEvidence limited to animal or cell studies.

We rate evidence conservatively. A dramatic headline number (like piperine's “2000%” boost to curcumin) is reported together with the study size and design, and we distinguish effects on a single meal from effects on long-term nutrient status.

Severity

Critical — a real risk of harm; talk to a clinician first. Caution — meaningful but manageable, usually with timing or dose. Note — minor or theoretical. Some rules escalate when you enter a dose above a threshold (for example zinc ≥ 50 mg/day with copper).

How the schedule is built

Each supplement has preferred slots (on waking, breakfast, lunch, dinner, bedtime) reflecting absorption and tolerability. The planner searches every arrangement of each group of related supplements and picks the one with the lowest total cost: preference, plus a large penalty for breaking a required spacing (e.g. iron and calcium 2 h apart, minerals 4 h from thyroid medication), plus a small penalty for splitting pairs that work better together (e.g. curcumin and piperine).

If a spacing cannot be met, the schedule shows a timing-conflict badge instead of hiding it.

Limitations

The dataset is not exhaustive and does not cover all prescription drugs. “No known interaction” is not the same as “safe”. Individual needs vary with age, sex, diet, genetics and health status. This tool is for information only and does not replace advice from your doctor or pharmacist.