A clinical trial in which patients are randomized to receive either an experimental drug or a placebo (a medicine with no active ingredients).

Ideally, such trials are ‘double-blinded’ so that neither patients nor the person administering the drug know what is being given.

Placebo-controlled trials are generally not done for antibiotics as this is considered unethical if alternative effective treatments already exist. Clinical trials of antibiotics usually compare a new drug with an existing drug or current standard of care.