No treatment vs treatment A vs treatment B vs both A and B. Is it ok for "both" to be a category? I want to estimate the effect of some treatments on an outcome. I am interested in the effect of treatment A, the effect of treatment B, and the effect of applying both treatments simultaneously.
I have data on who received which treatment and who received both. Would it be ok to run a regression with:

*

*An indicator variable for having received only treatment A

*and an indicator variable for having received only treatment B

*and an indicator variable for having received both

Having this "both" category smells like parameter dependency or something to me, so I thought I should ask...

You shouldn't need the indicator variable for having received both, otherwise you're good.
