PMS & the placebo effect: Why & how it works is reviewed in this article about a PMS clinical trial

A growing body of research suggests that  “open-label placebos” can still lead to positive health outcomes, and many past studies of open-label placebos give patients an explanation of why they might work.

A new study, published in BMJ Evidence-Based Medicine, showed that this explanation is important and even beneficial.150 participants were assigned to one of three groups: A no-treatment control, a placebo group with no explanation, and a placebo group where participants were informed about the demonstrated effectiveness of placebos for PMS in prior research. Participants  were also told about the  "conditioning process" by which placebos might work  since in childhood you connect taking a pill with some alleviation of symptoms, thererfore, when you take a placebo for PMS, it might also improve symptoms.

Those that received by a clear explanation of why the placebo might work had  a 79.3% reduction in PMS symptom intensity and an 82.5% decrease in how much those symptoms interfered with their lives. Placebo receipients without an explanation of how they work, reported a 50.4% decrease in symptom intensity and a 50.3% drop in life interference. Those with no additional treatment meaning no placebo had a 33% reduction in symptom intensity and a 45.7% decrease in life interference.

The decrease in symptoms even in the no-treatment group could be related to keeping a symptom diary, or the Hawthorne effect, a psychological phenomenon in which individuals alter their behavior due to their awareness of being observed. However, the placebo with explanation led to significantly better PMS symptom management than no treatment or placebo without explanation.

Realistically, we still don’t know why the act of taking a pill, even if you don’t believe in the medication’s therapeutic effect, can trigger a benefit. The fact that  this  study tries to understand  these mechanisms is very appreciated.