Placebo refers to medication or treatment that is inert which produces psychological benefit. Much like other scientific fields placebos are used in dentistry as a way to ascertain whether different procedures or treatments work on their own merit or due to an unknown variable.
Mechanism of the effect
The phenomenon of an inert substance resulting in a patient’s medical improvement is called the placebo effect. The phenomenon is related to the perception and expectation which the patient has; if the substance is viewed as helpful, it can heal, but if it is viewed as harmful, it can cause negative effects, which is known as the nocebo effect. The basic mechanisms of placebo effects have been investigated since 1978, when it was found that the opioid antagonist naloxone could block placebo painkillers, suggesting that endogenous opioids are involved.
Expectancy and conditioning
Placebos exert an “expectancy” effect whereby an inert substance which is believed to be a drug has effects similar to the actual drug. Placebos can act similarly through classical conditioning, where a placebo and an actual stimulus are used simultaneously until the placebo is associated with the effect from the actual stimulus. Both conditioning and expectations play a role in placebo effect, and make different kinds of contribution. Conditioning has a longer lasting effect, and can affect earlier stages of information processing. The expectancy effect can be enhanced through factors such as the enthusiasm of the doctor, differences in size and color of placebo pills, or the use of other interventions such as injections. In one study, the response to a placebo increased from 44% to 62% when the doctor treated them with “warmth, attention, and confidence”. Expectancy effects have been found to occur with a range of substances. Those who think a treatment will work display a stronger placebo effect than those who do not, as evidenced by a study of acupuncture.
Because the placebo effect is based upon expectations and conditioning, the effect disappears if the patient is told that their expectations are unrealistic, or that the placebo intervention is ineffective. A conditioned pain reduction can be totally removed when its existence is explained.[36] It has also been reported of subjects given placebos in a trial of anti-depressants, that “Once the trial was over and the patients who had been given placebos were told as much, they quickly deteriorated.”
A placebo described as a muscle relaxant will cause muscle relaxation and if described as the opposite, muscle tension. A placebo presented as a stimulant will have this effect on heart rhythm, and blood pressure, but when administered as a depressant, the opposite effect. The perceived consumption of caffeine has been reported to cause similar effects even when decaffeinated coffee is consumed, although a 2003 study found only limited support for this. Alcohol placebos can cause intoxication and sensorimotor impairment. Perceived ergogenic aids can increase endurance, speed and weight-lifting ability, leading to the question of whether placebos should be allowed in sport competition. Placebos can help smokers quit. Perceived allergens which are not truly allergenic can cause allergies. Interventions such as psychotherapy can have placebo effects. The effect has been observed in the transplantation of human embryonic neurons into the brains of those with advanced Parkinson’s disease.
Because placebos are dependent upon perception and expectation, various factors which change the perception can increase the magnitude of the placebo response. For example, studies have found that the color and size of the placebo pill makes a difference, with “hot-colored” pills working better as stimulants while “cool” colored pills work better as depressants. Capsules rather than tablets seem to be more effective, and size can make a difference. One researcher has found that big pills increase the effect while another has argued that the effect is dependent upon cultural background. More pills, branding, past experience, and high price increase the effect of placebo pills. Injection and acupuncture have larger effect than pills. Proper adherence to placebos is associated with decreased mortality.
Motivation may contribute to the placebo effect. The active goals of an individual changes their somatic experience by altering the detection and interpretation of expectation-congruent symptoms, and by changing the behavioral strategies a person pursues. Motivation may link to the meaning through which people experience illness and treatment. Such meaning is derived from the culture in which they live and which informs them about the nature of illness and how it responds to treatment. Research upon the placebo treatment of gastric and duodenal ulcers shows that this varies widely with society: those in Germany having a high rate placebo effect while those in Brazil a low one. Placebo effects in treating gastric ulcers is low in Brazil, higher in northern Europe (Denmark, Netherlands) and extremely high in Germany. But the placebo effect for hypertension is lower in Germany than elsewhere Social observation can induce a placebo effect such when a person sees another having reduced pain following what they believe is a pain reducing procedure.
The placebo effect can work selectively. If an analgesic placebo cream is applied on one hand, it will reduce pain only in that hand and not elsewhere on the body If a person is given a placebo under one name, and they respond, they will respond in the same way on a later occasion to that placebo under that name but not if under another.
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