Intent-to-treat is an analysis principle that keeps participants in the groups they were originally assigned to, even if they missed doses, stopped treatment, switched conditions, or dropped out.
Why it exists
Random assignment protects a trial because groups start comparable on average. If analysis later removes inconvenient participants, that protection weakens. People who stop a supplement may differ from people who tolerate it, adhere to it, or feel early benefit.
Intent-to-treat preserves the original comparison and asks a practical question: what happened when people were assigned to this strategy?
How it differs from per-protocol analysis
Per-protocol analysis includes only participants who followed the study plan closely. That can estimate what happened under high adherence, but it can also make results look cleaner than real use.
Both analyses can be informative when reported together. If intent-to-treat and per-protocol results disagree sharply, readers should look for dropout, side effects, poor adherence, or broken blinding.
Why missing data matters
Intent-to-treat does not solve missing data by itself. Researchers still need a defensible plan for unavailable outcomes, and that plan should be declared before analysis when possible.
The resulting confidence interval should reflect uncertainty rather than treating missing participants as if their outcomes were known.
How this affects evidence tier
A randomized controlled trial with clear intent-to-treat analysis usually supports a stronger evidence tier than a trial that quietly analyzes only completers.
For recommendations, intent-to-treat results are often closer to what a real user can expect because real adherence is imperfect.
Safety note
Intent-to-treat can make benefit estimates more realistic, but adverse-event review still needs direct safety reporting.