R help - Jul 2016 - Coefficients: (20 not defined because of singularities)

Hello Sir

I came across an old post of your discussing the singularity of the model
matrix, where the data matrix suffers from multicollinearity. You mentioned that
using a control variable with binary indicator is a possible option for that.

I wanted to ask you what is the correct remedy in case where we do not want to
drop the collinear variables? Actually, I?m trying to estimate the coefficient
of the binary variable, and it?s the same in both cases: including and not
including interaction terms. Should I interpret the coefficient of the binary
variable as the treatment effect or do I find another way to produce different
results in both cases?