Logical Reasoning

PT142 · S1 · Q6 While grapefruit juice is a healthy

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While grapefruit juice is a healthy drink, it has been discovered that a chemical in the juice affects how certain medicines are absorbed, with the result that normal medicinal doses act like higher doses.

Conclusion

The best medical approach would be to take lower doses of these medicines with prescribed amounts of grapefruit juice.

Evidence

It's always desirable to take the lowest effective dose of any medicine, and there is a chemical in grapefruit juice that affects how certain medicines are absorbed, such that it turns a normal dose into a "higher" dose.

Evaluate

Since grapefruit has a chemical that essentially augments the effects of certain medications, the author is thinking,

Whenever we're arguing with Plans / Recommendations, we try to think of how this Plan could fail to achieve its goal: - maybe it's not feasible - maybe people aren't incentivized to cooperate - maybe it will backfire in some way

Goal

Let's look for an answer that makes it sound like it's not feasible to do lower dose + grapefruit juice (i.e. some people have other conditions that won't let them take grapefruit juice / grapefruit juice isn't available year round), that makes it sound like the incentives are off (maybe people hate the taste of grapefruit juice so they would take their pill but then toss the grapefruit juice down the sink), or that makes it sound like the plan could backfire (people start experimenting with grapefruit juice to see if it can augment other medicines or give them amped-up symptom relief, and they accidentally harm themselves).

We can preface our reading of each answer choice with,

Which one of the following, if true, most seriously weakens the argument?

Correct
The amount of the chemical
Why this is right
This plan to do low dose + grapefruit juice probably won't work, because .... the variable rate of the supercharging chemical will make it too hard to dose properly. If one day you take your heart medicine + 6 oz of grapefruit juice and there happens to be 10mg of the medicine-boosting chemical, that will give you a very different medicinal effect then if the following day you take your heart medicine + 6 oz of grapefruit juice and there happens to be 20mg of the chemical. That extra chemical concentration could create dangerous dosing (if there's too much of the chemical) or ineffective dosing (if there's too little of the chemical).
Skill tested: Weaken · how this choice captures the argument's function is the move to repeat next time.
86% picked this
Grapefruit juice is less expensive
Strengthens, if Anything
The fact that the grapefruit juice is cheaper than the medicine almost has no effect, but if anything it would make this plan seem more feasible.
0% picked this
When scientists removed the chemical
No Impact
This answer if anything strengthens the idea that the chemical is the causal difference-maker. When we remove it, the augmenting effect disappears. But this was never in doubt. This was part of the background evidence that we're already accepting.
4% picked this
The chemical in grapefruit juice
No Impact
This just tells us how it is that the chemical in grapefruit juice augments medicinal strength. We don't really care about the specifics of how it does it. We only care about whether it seems wise to adopt a policy of pairing lower doses with a side of grapefruit juice.
5% picked this
Long before the chemical in
No Impact
The past status of what doctors used to say isn't really relevant to our current understanding about this chemical and the current plan under consideration. Until we discovered the chemical in grapefruit juice that was messing up medications, doctors probably had anecdotes about grapefruit juice messing things up and didn't know why but warned their patients to stay away from it. But now that we understand the chemical, this answer wouldn't really be relevant any more.
5% picked this

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