Why is the reversibility of any treatment effects earth-shattering and what if the effects are not reversible?

Why is the reversibility of any treatment effects earth-shattering and what if the effects are not reversible?
Effects of treatment with most hormones including insulin are reversible.
Actions of drugs similar to a)sympathomimetics 2)sympatholytics 3)parasympathomimetics and 4)parasympatholytics are also reversible.
This reversibility makes it confident to predict and treat some untoward effects of drugs.
When actions of some drugs are not reversible antidotes must be kept geared up or provisions for symptomatic treatment of complications should be made available.
medicine and robustness guarantee correctness , is for informational purposes only proposal or treatment for any medical conditions.