The difference between medicine and poison is the dose

May 08, 2025 8:52 AM
Jun 12, 2025 4:38 PM

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The difference between medicine and poison is in the dose. Too much of a beneficial substance can be harmful or lethal, and a tiny amount of a harmful substance can have beneficial effects. It’s necessary for doctors to give patients doses of medication that are big enough to be effective but not so big as to be dangerous. Prescribing a bit less than the harmful amount isn’t much good. A patient could take too much or take their doses too close together.

So pharmacologists calculate the minimum effective dose: the lowest possible amount of a medication to achieve a meaningful benefit in the average patient. Then they calculate the maximum tolerated dose: the largest amount an average patient could take without suffering harm. For example, a vaccine contains the minimal possible dose of a virus necessary to get the body to produce an immune response. Too much could cause actual illness; too little would not be protective. Knowing this window means doctors can ensure a margin of safety by starting with a low dose they still know is likely to work.