It's a bit complicated, but let me try. First, I would rewrite as follows (to make the sentence more clear) :
"It was just a small, initial study, and the study did not have have a control group (i.e., a separate group of people who, for example, got a placebo shot)."
In an initial study, the sample size of the study participants is usually small. At times, during this stage, the researchers do not employ a usual "double-blind" experimental method where 1/2 of the participants are given "fake" medicine or treatment, i.e., a placebo. This kind of "first" study is an attempt to get a "quick and dirty" indication of the effectiveness of a medicine or treatment.