Actually, you can....
There was some really interesting research done that showed a stronger placebo effect if the taker thought the placebo was more expensive than if they thought it was cheap. Tell them its a trial version of a $500/tablet drug and the effect is really strong. Tell them its a generic version of something you can buy over the counter for a few cents and the effect is lower.
The effect is also stronger if you tell them its "extra strength" or "premium" or words like that.
The brain is a weird thing.
Cheers
Dave