I wonder if the outcome of the study could also be affected (in part) by emotional states associated with past uses of acetaminophen.
In the past, there have been people close to me that used aromatic "remedies" like essential oils for headaches and other ailments, to the point that now whenever I smell those scents, I unconsciously start feeling as though I am (or someone near me is) sick or in pain. I suspect there may be similar effects (conscious or not) with drugs that have historical associations in the minds of participants in the study. Rather than an associated smell, perhaps an altered state of body/brain chemistry could make similar memorable impressions.
Interesting to me -- as a kid, the only place I smelled lily flowers was at funerals. Their pungent and slightly unpleasant odor I thought was enbalming fluid, or something else associated with dead bodies. I can't smell them to this day without immediately associating them with the pallid, sunken skin of dead, elderly white folks.
In the past, there have been people close to me that used aromatic "remedies" like essential oils for headaches and other ailments, to the point that now whenever I smell those scents, I unconsciously start feeling as though I am (or someone near me is) sick or in pain. I suspect there may be similar effects (conscious or not) with drugs that have historical associations in the minds of participants in the study. Rather than an associated smell, perhaps an altered state of body/brain chemistry could make similar memorable impressions.