# What is the process of calculating if a molecule is helpful and/or harmful to an organism?

From reading about pharmacology through the years I synthesized from my own prior research that `What is the process of calculating if a molecule is helpful and/or harmful to an organism` is this:

1. A researcher gives a Dose Of Drug (DOD) to an organism with a biochemical problem; from one molecule up to some reasonable amount
2. The drug might have some Minimal Effective Dose (MED) by mean of treatment; likely with biological half-life.
3. The first dose that is both Treating and Harming is TaHDOD, and somewhat larger dose would be lethal.
4. A ratio between MED to TaHDOD, is a Margin Of Safety (MOS).
5. MOS translated into a dosage is a Therapeutic Index (TI).
6. To calculate TI, two different reasonable dosages are given to one group of organisms (in different, isolated periods) with the same biochemical problem
7. The dosage that helps in at least 50% of the cases and isn't significantly harmful is within MOS.

More dosage == More risk ; due to Law of Mass Action.

## My problem

I am having a problem to understand what is the process of calculating if a molecule is helpful\harmful to an organism in general and how to understand how biochemists calculate ratio between MED to TaHDOD.

## My question

What is the process of calculating if a molecule is helpful and/or harmful to an organism?

• This is very broad. The process will differ significantly depending on the type of drug being tested. – Carey Gregory Jan 16 at 20:43
• Do you mean like Dose response? – JMP Jan 17 at 8:35
• Hello @JMP I guess I meant dose because I'm not sure I understood what the OP meant there by `Dosage is the rate of application of a dose` - I meant to dose a a weight (say, 1 microgram or 1 milligram) so I guess we go with dose. – JohnDoea Jan 17 at 8:37
• I didn't notice you changed in many places from dose to dosage; if it's the correct form in English then of course I have no objection to keeping it... – JohnDoea Jan 17 at 8:40
• Dose and dosage are considered interchangeable: en.wikipedia.org/wiki/Dose_(biochemistry) – JMP Jan 17 at 8:51