To test the effectiveness of an allergy drug, scientists begin with a pool of 12,000 allergy sufferers. One randomly selected group of 6,000 subjects is given the drug, and the other 6,000 are given a pill without the active ingredient. They are asked to report their allergy symptoms after 1 week, 1 month, and 3 months of treatment, and samples are also taken to measure the levels of histamines (allergy-related compounds) in the blood. What group is receiving the experimental treatment in this study?