Clinical trials do use placebos all the time, even when studying things that don't involve pain.
Somewhat notoriously some trials give patients a placebo that's actually another drug, as otherwise people could unblind themselves by not suffering side effects. The COVID vaccine trials did this. It doesn't make sense if you think the placebo effect only influences perception of pain, as otherwise you could lose the placebo entirely and double your statistical power (compare against a synthetic control group).
Somewhat notoriously some trials give patients a placebo that's actually another drug, as otherwise people could unblind themselves by not suffering side effects. The COVID vaccine trials did this. It doesn't make sense if you think the placebo effect only influences perception of pain, as otherwise you could lose the placebo entirely and double your statistical power (compare against a synthetic control group).