You're describing an active-control trial, not a placebo-controlled trial. In a trial of drug A (current standard of care) vs. drug B (new agent), there will us

You're describing an active-control trial, not a placebo-controlled trial. In a trial of drug A (current standard of care) vs. drug B (new agent), there will usually be 2 placebos involved. Participants will be randomized to receive drug A + placebo B or, conversely, placebo A + drug B. Typically the manufacturer of each drug is in the best position to produce an identical appearing placebo for each pill.