Pills and Potions

[Monica]

In the following multiple choice exercise:
It's unlikely that using vast amounts of pills and ... will delay the ageing process.
a tablets b potions c exercise d injections
The answer key gives "potions" as the only correct answer. However, I don't see why "tablets" is incorrect, especially as pills is fine and they're pretty similar. Can someone help me with this one, please?

[Mister Micawber]

.
You're right logically, Monica, but it is a matter of collocation-- 'pills and potions' is a set phrase. In fact, we hardly use the word 'potions' alone these days for medicines.
.
_________________
Native English teacher at Mister Micawber's

[Molly]

And "potions" helps express the cynicism of the speaker, there.