Effective Dose 50

By Tabitha Mishra
Last updated: February 21, 2022

What Does Effective Dose 50 Mean?

The median effective dose (ED50) is a pharmacological term for the dose or concentration of a medication that produces a therapeutic effect in 50% of subjects taking it.

Safeopedia Explains Effective Dose 50

The median effective dose is determined during new drug clinical trials and in studies of existing drugs. The precise ED50 dose can vary across different populations and groups of subjects, since the effects of a dose can be affected by factors such as age, health status, or interactions with other medications.

While a drug's ED50 is not necessarily the right dose to prescribe an individual patient, it can be a useful guide for physicians deciding on an appropriate starting dose.

Whole Animal Experiments Vs. Population Studies

The precise meaning of ED50 depends on the type of study it refers to.

In a whole animal experiment or patient study, where there is a single subject, the median effective dose refers to the concentration at which the drug produces 50% of its maximal effect. In other words, it is not the median dose that produces an effect but the dose at which a median effect is produced.

In population studies, there is no such dose. Given individual factors and difference susceptibilities to a drug, there will not be a single precise concentration that produces the exact median effect across all patients. Instead, ED50 in this context refers to the median concentration that produces its desired effect in half of the test population.

Clinical Research Phase Studies

Before beginning clinical trials, drug developers are required to submit an Investigational New Drug (IND) application to the Food and Drug Administration (FDA). Clinical trials involve four phases:

Phase 1

Initial safety trials on a new medicine, attempting to establish the dose range tolerated by volunteers. This phase gathers information about how a drug interacts with the human body.

Phase 2a

Pilot clinical trials to evaluate the efficacy and safety in selected populations of patients with the disease or condition to be treated, diagnosed, or prevented.

Phase 2b

Usually the most rigorous demonstration of a drug's efficacy. These are sometimes referred to as pivotal trials since they make or break the drug’s effectiveness. The ED50 is calculated from data obtained during the trial. The drug will not continue in clinical trials if it does not meet the effectiveness goal reflected from data or the calculated ED50.

Phase 3a

Trials conducted after efficacy of the medicine is demonstrated. Phase 3a clinical trials generate additional data on both safety and efficacy. The trials are conducted in relatively large numbers of patients in both controlled and uncontrolled trials. Clinical trials are also conducted in special groups of patients.

Phase 4

This phase is carried out once the drug has been approved by the FDA during the post-market safety monitoring. The drug safety and efficacy may be evaluated for a significant time after it is on the market.

The ED50 may be revised based on Phase 4 data. Different formulations, dosages, duration of treatment, medicine interactions, and other medicine comparisons may be evaluated. New age groups, races, and patient demographics can also be studied.

Other Dosage Terms

Other dosage terms that can be used in similar contexts to ED50 include:

  • ED95 – the dosage that produces a therapeutic effect in 95% of subjects
  • Median toxic dose (TD50) – the dosage that produces a toxic effect in 50% of the subjects
  • Median lethal dose (LD50) – the dosage that is lethal to 50% of subjects


Median Dose

Median Effective Dose

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