Getting Started with LLMs: A Physician's Guide to the AI Revolution

Introduction

We are living through a technological inflection point that rivals the introduction of the internet or the smartphone. For physicians, Artificial Intelligence (AI) - and specifically Large Language Models (LLMs) like ChatGPT, Claude, and Gemini - represents a fundamental shift in how we access information, draft documentation, and even approach clinical reasoning.

If you've felt overwhelmed by the "AI hype" or unsure where to begin, you are not alone. Medicine is a field grounded in evidence and caution, while AI seems to move at breakneck speed. This guide is designed to bridge that gap. We will strip away the jargon and focus on what you actually need to know to start using these tools safely and effectively in your practice today.

What Are Large Language Models?

At their core, Large Language Models are sophisticated pattern recognition engines trained on vast amounts of text data - essentially a significant portion of the public internet, including books, articles, code, and websites.

The "Next Token" Prediction

Think of an LLM as a super-powered autocomplete. When you type a query, the model isn't "thinking" in the human sense. Instead, it is probabilistically predicting the next most likely word (or "token") in a sequence based on the patterns it learned during training.

If you type: "The patient presented with a chief complaint of..." The model analyzes its training data to understand that words like "chest pain," "shortness of breath," or "abdominal pain" are statistically likely followers in a medical context.

Why "Large"?

The term "Large" refers to the number of parameters - the internal variables the model uses to make these predictions. Modern frontier models have hundreds of billions, potentially trillions, of parameters. This massive scale allows them to do more than just complete sentences; they can reason through complex problems, summarize dense medical literature, write code, and mimic specific writing styles with uncanny accuracy.

The Landscape: Major Players in 2026

The AI market is crowded, but for clinical and academic purposes, a few key players dominate the field. Here is a breakdown of the tools you should know:

1. ChatGPT (OpenAI)

• Best For: General versatility, reasoning, and coding.
• The Vibe: The "Swiss Army Knife." It's widely available and incredibly capable.
• Key Feature: The "o1" and "o3" series models (reasoning models) are particularly good at complex logic, which can be useful for differential diagnosis brainstorming (with caveats).

2. Claude (Anthropic)

• Best For: Writing, summarization, and tone management.
• The Vibe: The "Empathetic Professional." Claude is often cited by physicians as sounding more human and less robotic than ChatGPT. It excels at drafting patient communication and summarizing long papers without losing nuance.
• Key Feature: "Artifacts" allow you to view code, documents, and diagrams in a side panel, making it great for building workflows.

3. Gemini (Google)

• Best For: Multimodal input and Google ecosystem integration.
• The Vibe: The "Researcher." Because it is plugged directly into Google's vast information ecosystem, it can be very effective at retrieving real-time information.
• Key Feature: Deep integration with Google Workspace (Docs, Drive, Gmail) makes it a seamless choice if your institution uses Google.

4. Perplexity

• Best For: Search and citations.
• The Vibe: The "Librarian." unlike the others, which generate text from internal training, Perplexity acts as a search engine that reads the web and synthesizes an answer with citations.
• Key Feature: Every claim is footnoted. For a physician, this transparency is non-negotiable.

How to Choose Your First Tool

If you have never used an LLM before, start here:

1. For Search & Learning: Use Perplexity. It's the safest bridge from "Googling" to "AI Search." You can verify sources immediately.
2. For Writing & Admin: Use Claude. Try pasting a de-identified, jargon-heavy note and asking it to "rewrite this as a patient-friendly letter at a 6th-grade reading level." You will be amazed.
3. For Complex Logic: Use ChatGPT (Plus). If you want to brainstorm research ideas or structure a complex grant proposal, its reasoning capabilities are top-tier.

Your First Steps: A Practical Exercise

Let's move from theory to practice. Open one of the tools mentioned above (the free versions are fine for this) and try this prompt.

The Task: Explain a complex medical concept to a patient.

The Prompt:

"I am a radiation oncologist. I need to explain the concept of 'fractionation' in radiation therapy to a patient who is anxious about coming in for treatment every day for six weeks. Please draft a script I can use. Use a comforting, professional tone. Use an analogy related to sun exposure to help them understand why we don't give the whole dose at once."

What to Look For:

• Tone: Is it empathetic?
• Accuracy: Is the analogy sound?
• Clarity: Is the language accessible?

You will likely find that the output is 80-90% usable immediately. The remaining 10-20% is where your expertise comes in - editing, refining, and validating.

The Golden Rules of AI in Medicine

As you begin exploring, adhere to these three core principles:

1. Human in the Loop (HITL): Never copy-paste AI output directly into a medical record or patient communication without reading and verifying it. AI can hallucinate (make things up). You are the licensed professional; the AI is just a drafter.
2. Zero Patient Data: Unless you are using an enterprise-grade, HIPAA-compliant instance provided by your institution, never input Protected Health Information (PHI) into a public chatbot. No names, dates of birth, or MRNs. See our safety guide for more details.
3. Trust but Verify: If an LLM cites a paper or a guideline, verify it exists. Hallucinations often look like plausible citations.

Conclusion

The goal of using AI in medicine isn't to replace the physician, but to unburden them. By automating the drudgery - the drafting of letters, the summarizing of charts, the administrative overhead - we can reclaim time for what matters most: the patient-physician relationship.

Start small. Pick one tool. Try one prompt. Welcome to the future of practice.