I'm no expert but I feel like it could be argued.
I'm 100% sure, for example, that if a company hires a person in a desk job who presents one day with back complaints, then they're bound by law to provide that person with a chair that allows them to do their work with their condition, an orthopedic chair if you will. And that would definitely be an allowable business expense for a medical intervention. I've worked with such people in the past, I've also worked with unusually short and tall people who need whole new suites of equipment like specialist desks and chairs just to be able to do the basics. Maybe it's not a legal requirement, but most large companies will comply with requests like that, and most certainly write it off.
It then stands to reason that a self-employed person would be able to make a similar claim. For example a person with a missing leg could live comfortably without a prosthetic leg, but one day decides they want to be a lumberjack, so now a prosthetic leg is a necessary business expense but purely only for business use - he only wears the leg when he's at work and has no need for it otherwise. Again, a medical device is an allowable business expense in this scenario. I don't see the government arguing in court that an inspiring lumberjack like that should be fined because he could theoretically technically cut down trees without the prosthetic leg if he really really gave it a jolly good go.
Then from there's it's not much of a stretch to go to a
MC patient. If, for example, their
MC is prescribed for social anxiety, but they're actually happy to live with social anxiety as a hermit... and therefore only needs to interact with people purely for business purposes, and therefore only needs their prescription for business purposes, then I don't see how it's any different from the legless lumberjack who can't cut down trees without a prescribed prosthetic leg - you're a socially anxious complaints call handler who can't dispatch irate clients without prescribed medical cannabis.
That combined with the fact that you're allowed to divvy up your electricity bill and home expenses for the business portion of their use means I don't see why you can't estimate the portion of your
MC that wouldn't be necessary if it wasn't for work requirements interacting with your symptoms.