Drug efficacy: How to tell if a medicine really works

Here’s a blunt fact: a medicine can look great in a shiny trial but do very little for people in everyday life. Knowing how to read results and spot what matters lets you make smarter choices about treatments. This page gives clear, practical steps to judge drug efficacy so you can talk confidently with your doctor.

What "efficacy" really means

Efficacy is about performance in controlled trials. Effectiveness is how it works for regular people. Trials try to limit confounders—so they show potential, not always real-world benefit. When you read a headline claiming a drug "cuts risk by 50%," ask: 50% of what? Often that’s relative risk. The absolute benefit can be tiny.

Look for these specifics: the primary endpoint (did the trial measure survival, symptom relief, or a lab marker?), the size of the study, and how long patients were followed. Short trials or surrogate endpoints (like lowering a blood marker) can be useful, but they don’t always mean you’ll feel better or live longer.

Quick checklist to judge a drug

Use this short checklist when you see a claim about a drug:

- Endpoint: Is it meaningful to patients (survival, quality of life) or just a lab value?

- Absolute vs relative benefit: Ask for absolute risk reduction or number needed to treat (NNT).

- Side effects: How common and how severe? Check withdrawals due to adverse events.

- Study size and length: Bigger and longer trials give more reliable answers.

- Conflicts of interest: Who funded the study? Independent trials are stronger.

- Peer review and replication: Has the result been confirmed by others or in meta-analyses?

Also check real-world evidence: post-marketing reports, registries, and observational studies can reveal rare harms or show if patients outside trials get similar benefits.

Subgroups matter. Some drugs help certain ages or people with specific conditions more. But beware of small subgroup claims—those findings often don’t hold up.

Practical example: If a cholesterol drug lowers a marker but doesn’t reduce heart attacks or death in trials, that’s less useful than a drug that cuts real events even if the marker shift looks modest.

Finally, personal factors change the math. Your age, other illnesses, kidney or liver function, drug interactions, and how likely you are to take the drug exactly as prescribed all affect real benefit.

Questions to ask your clinician

- What outcome did the trials measure and how big was the benefit for people like me?

- What are the most common and most serious side effects?

- How long do I need to take it to see benefit, and how will we monitor it?

- Are there cheaper or safer alternatives that work just as well?

Use these tips to cut through hype and focus on what matters: real, measurable benefits and risks for you. If something feels unclear, ask for plain numbers—absolute risk, NNT, and expected side effects. Those numbers tell the real story.