Four widely used platforms, four different starting propositions, and a practical question underneath the comparison: which fits which part of the reader's work. This guide is published by iatroX and includes iatroX among the four; it states that plainly so a reader can weigh it.
Four starting propositions
OpenEvidence: evidence retrieval, literature-led, built around peer-reviewed sources. ChatGPT: broad clinician assistance, general-purpose, with ChatGPT for Clinicians as a verified-professional tier and Study Mode as a tutoring mode. Heidi: documentation workflows, with a product that explicitly spans evidence, scribing and dictation. iatroX: integrated clinical learning, free clinical reference grounded in UK guidance plus question banks, Tutor, planner, simulations and CPD. The propositions increasingly overlap, Heidi includes evidence, ChatGPT tutors, OpenEvidence expands into workflow, and the comparison below treats overlap as real rather than pretending each product stays in its lane.
Adoption and access panel
iatroX: 1 million uses, over 50,000 verified clinicians, 40 countries, primarily UK, over 15% of UK GPs, per iatroX platform data, September 2026; Ask-iatroX free, all-access £99 a year or £29 a month. OpenEvidence: one million clinical consultations in a single day on 10 March 2026, per its announcement; free for verified US healthcare professionals. ChatGPT: ChatGPT for Clinicians free for verified US physicians, nurse practitioners, physician assistants and pharmacists; general tiers globally. Heidi: approximately 2.74 million patient visits supported in the week shown on its homepage when checked; free clinician tier for qualifying trainees and students. Geography and units are kept visible deliberately: a cumulative clinician count, a single-day consultation figure and a weekly visit count are not the same measure.
A clinical-information task
The defined task: a fictional question with a UK-specific answer, the first-line pharmacological management of a newly diagnosed adult with a common long-term condition under current NICE guidance, where UK and US recommendations are known to differ. The assessment criteria: does the platform cite a source, does the source support the specific claim, is the jurisdiction correct for UK practice, and is the answer clear enough to act on. This guide does not fabricate observed results; the task is stated so that it can be run, and results will be published from an actual run with the date and platform versions recorded. A reader can run the same task today and compare source support, relevance and clarity directly.
A learning task, separately
The defined task: a learner answers a question incorrectly and wants to understand why. On OpenEvidence, the learner can search the underlying evidence but has no question-anchored tutoring. On ChatGPT Study Mode, the learner can be guided through the reasoning, genuinely, with the tutoring anchored to whatever they choose to ask. On Heidi, this is not the product's job. On iatroX, the Tutor opens on the specific missed question, asks a targeted follow-up, identifies the misconception, and the planner schedules a revisit and, where relevant, a simulation applies the correction under pressure. Answering a clinical question and managing a structured learning pathway are different capabilities, and only one of the four is built around the second.
iatroX's educational breadth, explicitly
The Tutor, question-anchored rather than open-ended. The study planner, exam-date-aware and adapting to performance. And iatroX Simulations, eighteen clinician-reviewed examination-specific tracks with transcript-linked feedback and Tutor-led follow-up, included in the all-access subscription. These are the capabilities that distinguish an integrated learning platform from an evidence engine, a general assistant or a documentation tool, and they are given dedicated attention here because the comparison is otherwise misleading.
Use together or replace?
A reader may reasonably choose Heidi for documentation and iatroX for reference and learning; the two do different jobs and neither replaces the other. A reader eligible for OpenEvidence may use it for literature synthesis and iatroX for UK-guideline answers and structured learning. A reader may use ChatGPT for drafting and general questions and iatroX for the learning pathway. Where iatroX can consolidate is the learning tools: a reader running a separate question bank, a separate tutor and a separate simulation product may replace all three with one subscription. Where it cannot is documentation, and this guide does not claim otherwise.
Why the units matter more than the numbers
A reader comparing the adoption panel above could conclude that OpenEvidence or Heidi is far larger than iatroX, and in throughput terms on their own measures that may be true; they could equally conclude that iatroX's verified clinician base is the most relevant figure for UK practice, and that may also be true. Neither conclusion follows from a single number, because the platforms measure different things. This guide keeps the units visible so the reader can decide which measure matters for their own decision, rather than presenting a ranking the underlying data does not support.
Frequently asked questions
Which of the four is best?
Each is best at its own starting proposition; the practical question is which part of your work each one fits.
Does iatroX replace Heidi?
No: Heidi documents consultations, iatroX answers clinical questions and supports learning, and many clinicians use both.
Has the clinical-information task been run?
The task and criteria are defined here so they can be run and results published from an actual run; this guide does not invent results.
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