Say I have an observational dataset over 20 years with blood-pressure measured each year for 1000 men.
Each year a decision is made whether to start antihypertensive drug A, drug B or continue without medication. This decision is based on the blood-pressure, but the exact bloodpressure threshold is left at the discretion of the treating physician.
Moreover, the drugs can also be discontinued or changed from $A->B$ or $B->A$ based on the blood pressure.
Is there a method that allows me to disentangle the isolated effect of bloodpressure from treatment with drug A or drug B on outcome (Dead/Alive)?
Would a marginal structural model allow such complexity ?