Probably not without the researchers telling you. When patients are asked which group they thought they are in, most believe they are receiving the active treatment. Only a small number say they can't tell or thought they were in the sham (pretend) treatment group.
Studies show many people in the control group (group that doesn't get real treatment) get better anyway. This is called a placebo effect. In these studies, patients in both groups are followed for months to years after the treatment. The researchers look for long-term effects in order to measure the treatment against the placebo effect.