Common Toxicity Criteria (CTC), also referred to as the Common Terminology Criteria for Adverse Events (CTCAE), is a standardised classification of side effects used in assessing drugs for cancer therapy. It is a product of the National Cancer Institute. Currently version 4.0 is in use, released in 2009. Most US and UK drug trials base their observations on this system which has a range of grades from 1-5. Specific conditions and symptoms may have values or descriptive comment for each level, but the general guideline is:

1 - Mild

2 - Moderate

3 - Severe

4 - Life threatening

5 - Death.