Thanks for asking about the issue of potential heart damage. We discuss this in chapter 6 of the hardcover on pages 260 and 261. As a quick summary, while it will always be possible to come up with a pharmacological or animal-based model (where amounts of active substance often far exceed the dose level we use for microdosing), for now we are going to stick with the real-world evidence on this one, which is that there aren’t any reported cases or known problem.

We can’t, of course, disprove the possibility that some day in some circumstances microdosing will occasion heart damage through something along these lines, and indeed, scientific modeling may help us determine and avert any potential harm vectors ahead of time. But so far, we haven’t seen any real-world evidence of this being a problem, and for us real-world evidence always wins out.

If such real-world evidence turns up, we’d be the first to want to know everything about it, and what cautions might need to be taken or which population(s) really just shouldn’t microdose. (Needless to say, lots of things that cause considerable damage are regularly engaged in by human beings.) But until that time, perseverating over this possible danger will likely do more harm than good, and could even produce its own nocebo effect, discussed on p. 239:

The opposite of placebo is “nocebo,” where someone’s negative expectations regarding an inert treatment cause a negative effect. A wonderful example is a baseball game with a dozen hot dog stands throughout the ballpark. At some point the PA system announces that people who ate at one of the hot dog stands are getting sick. This causes a dramatic rise of sudden upset stomachs and nausea throughout the ballpark among all the hot dog eaters, since everyone assumes it might have been their hot dog stand.

Here we will shortly describe the different types of anxiety, and which types microdosing may not be helpful for.