Side Effects in Clinical Trials

There is a special vocabulary for talking about side effects in clinical trials. The side effect of a treatment during clinical trials is called an Adverse Event (AE). The National Cancer Institute (NCI) has established a standardized way to measure the seriousness of an adverse event. This is called the Common Toxicity Criteria for Adverse Events (CTCAE). The complete CTCAE can be found at the NCI website:

Adverse events are graded on a scale from 1 to 5. (Grade 0 refers to not having a symptom or problem, so someone with grade 0 pain has no pain at all.) Grade 1 adverse events are mild and generally not bothersome. Grade 2 events are bothersome and may interfere with doing some activities but are not dangerous. Grade 3 events are serious and interfere with a person’s ability to do basic things like eat or get dressed. Grade 3 events may also require medical intervention. Grade 4 events are usually severe enough to require hospitalization. Grade 5 events are fatal.            

Most clinical trials and doctors focus on grade 3 or higher events, because those are the most dangerous. Grade 2 events however, can significantly impact the patient’s quality of life, even if they are not medically dangerous. For example, a grade 1 headache is mild. A grade 2 headache keeps the patient from doing things like shopping or cooking. A grade 3 headache keeps the patient from getting out of bed even to go to the bathroom.