“…Placebo effects are readily obtainable in rodents (Guo et al 2011, Herrnstein 1962, Woods & Ramsay 2000 and humans by pharmacological conditioning, which involves repeated pairing of drugs with drug cues, usually over several days, and then testing by delivering the cues alone. Such procedures can produce effects on hormonal and immune responses (Goebel et al 2002, Schedlowski & Pacheco-Lopez 2010, which after conditioning appear to be insensitive to verbal instructions about the treatment and, thus, presumably to patients' beliefs (Benedetti et al 2003b, Wendt et al 2013. Similarly, placebo analgesic responses become stronger and more durable with longer conditioning (Carlino et al 2014, Colloca et al 2010, Colloca et al 2008a.…”