8/16/16 Placebo Effect - Willett Flashcards
placebo/nocebo effect definition
non-specific or contextual effects of a therapy
can be POSITIVE (placebo) or NEGATIVE (nocebo)
conceptualizing placebo effect
- no treatment effect [Hawthorne effect]
- placebo effect
- treatment effect
types of placebo treatments
most effective?
medication
surgery
physical/alternative therapy
psychosocial effects
SHAMS are far better than placebo pills
- sham surgery/acupuncture/injections/topical treatments are more effective than pills
what outcomes are most influenced by the placebo effect?
GRADED vs binary
SUBJECTIVE vs objective
magnitude of influence
WHY/HOW?
- half or more of medication benefit (esp pain/depression)
- up to 30% of patients discontinue placebo due to side effects
WHY/HOW?
- activation of brain areas
- changes in nt levels
- expectations, experiences, conditioning
- genetic predisp (esp to effectiveness of pain placebos)
- context (cost, color, setting)
- provider-pt relationship
examples of placebo effect:
neurotransmitter changes
- response to pain placebos blocked by naloxone (narcotic blocker), rimonabant (cannabinoid blocker)
- Parkinson pill placebos and sham surgery cause changes in functional MRI
- antidepression placebos and pain placebos cause changes in brain metabolic activity on functional MRI
how do expectations contribute to placebo/nocebo effect?
- post op patients: open vs “hidden” painkillers
- opiod admin to 7/10 pain scale
- college students with Ritalin placebo
- 3km athletes with “epo”
postop patients getting painkillers via either open injections or IV through which nurse will admin a dose (but cant see when)
- open treatment group needs less drug AND gets better pain relief
subjects asked to indicate 7/10 pain when heat applied during 4 phases [saline-opiod, not announced-opiod, announced-opiod, TOLD THEM DISCONTINUED]
- lower pain experienced with announcement
- pain came back up to baseline when told it was discontinued (NOCEBO effect)
college kids with Ritalin placebo
- placebo takers felt higher intellectual efficiency/energy, “high”, “stimulated” (placebo), also more dysphoric though (nocebo)
15 elite athletes offered “legal epo-like substance” in a crossover experiment
- placebo ran almost 10s faster!
nocebo expectations:
aspirin with side effect consent forms
placebo controlled trial with some forms listing “GI irritation” as side effect, some forms listing “generally well tolerated”
- GI irritation group had more GI effects! (19% vs 3%)
- number of people withdrawn from trial by physician for severe GI effects were same in both rgroups!
context/cost expectations:
2.50 vs 0.10 cost for a pill
85% of patients receiving expensive pill reported pain relief
61% of patients with cheap pill reported pain relief
**implications for healthcare cost containment!!!
sham acupuncture trial
CHRONIC KNEE PAIN
3 arms of study and outcomes
- frequent MD visits
- traditional acupuncture (0.5-3.5 cm insertion at traditional sites with manipulation)
- sham acupuncture (<.5 cm insertion at nontraditional sites with no manipulation)
“success” = 36% decrease in validated pain scale
best outcome :
- MD 29%
- traditional 53%
- sham 51%
studies and placebo
- what studies need a placebo to be valid?
- what determines this?
- how close should placebo be to tested therapy?
- in which studies would it be unethical to have a placebo arm?
studies with graded, subjective outcome NEED a placebo arm for validity
- OUTCOME is the major determinant of whether you need a placebo or not!
should try to make placebo and treatment undistinguishable
unethical if/when:
- credible placebo would be unethical (sternotomy)
- established treatment exists that is KNOWN to have major effect on death/disability in long term
therapeutic equipoise : you should be willing to sign up for your own study
