why is the reversibility of any treatment effects important and what if the effects are not reversible?

Answer 1

Effects of treatment with most hormones including insulin are reversible.
Actions of drugs like a)sympathomimetics 2)sympatholytics 3)parasympathomimetics and 4)parasympatholytics are also reversible.
This reversibility makes it easy to predict and treat some untoward effects of drugs.
When actions of some drugs are not reversible antidotes must be kept ready or provisions for symptomatic treatment of complications should be made available.