The placebo effect is a bane of clinical trials. A drug is considered ineffective if it is only as good as a placebo. And placebo can be quite good. Intriguingly, the placebo effect in clinical trials has been getting stronger over the past few decades. Lately, placebo has been receiving a lot of attention from researchers.
A rigorous study just published in the journal Pain looked at the effect of a placebo when patients were clearly told that they are taking a placebo. These patients were compared to those who were given a placebo in a double-blind study of peppermint oil capsules for irritable bowel syndrome (IBS). These two different types of placebo were compared to a control group of patients who were not given any pills.
Participants treated with an open-label placebo and a double-blind placebo reported similar and clinically meaningful improvements in IBS symptoms. These improvements were significantly greater than in those who were not given any pills. The results were statistically significant for the primary outcome measure (IBS Symptom Severity Scale) as well as for mean global improvement scores.
Twice as many patients in the double-blind placebo group had side effects (mostly gastrointestinal, such as heartburn) than those in the open-label placebo. It is probably because the first group was told about the possible side effects of peppermint oil.
The authors concluded that an open-label placebo “could play a role in the management of patients with refractory IBS”.
Just like migraines, IBS involves central sensitization and hypersensitivity of the nervous system. And just like with migraines, placebo response in clinical trials of IBS tend to be high. This is not to suggest that these conditions are psychological. Especially with migraines, the biological basis is well documented. Psychological factors, however, cannot be ignored. About 40% of patients with chronic pain, including migraines, have a history of emotional, physical, or sexual abuse. Post-traumatic stress disorder of other types also causes hypersensitivity of the central nervous system. Psychological factors can even be the cause of such potentially deadly conditions as broken heart syndrome (Takotsubo cardiomyopathy). It is likely that the placebo effect is stronger in conditions where psychological factors are more pronounced.
It is considered unethical to prescribe a placebo to patients without telling them that they are getting a placebo. This latest study suggests that some patients may improve even if they know that they are taking a placebo.
I do prescribe herbal supplements such as feverfew and boswellia and on a rare occasion, a homeopathic remedy, all of which lack rigorous proof of their efficacy. For that matter, many drugs we prescribe for migraines lack such definitive proof. I would suggest that we should first prescribe less harmful unproven remedies rather than unproven prescription drugs.
