Why is randomization important in clinical trials?

When you use the term drug trials I assume that you are talking about tests of new drugs on actual people to determine the actual effect or effectiveness of the new drug.

They are random for various reasons. The main reason is that the testers want to get an accurate idea of how they would work when used in the general population.

They have to account for as many variables as possible to account for different conditions. For example the tests may give different results if all of the subjects were male, or female.

Results can also be effected by the time that the tests are administered. The time of day or the time of year. Cold weather may cause changes in body chemistry that effects the way that the body handles the drug, as can hot weather, etc.

Age can be a factor because as we age our bodies change the way that they produce certain hormones and perform bodily processes. all of these factors can have an effect.

If you pick people of all the same race, same part of the country, same gender, same age etc., you might get results that will be different from results from other people.

When you use completely random trials you hopefully eliminate all or at least most of the outside variables that will have an influence on the test results so that you can get a truer and more accurate picture of what to expect from the use of the drug.