I agree with
A young infant cannot open a bottle or guide medication to their mouth, so the main danger of medication is that two adults in the household will each give them a dose. Childproof bottles won't do a damn thing about this; the only fix is for the adults to communicate somehow. In my experience, this is the most common way for a child to receive unneeded medication. (ETA: Several studies back me up-- in a study done in British Columbia, link here in PDF, it reports that there are NO confirmed deaths from acute poisoning-- that is, a single dose-- and that most serious consequences come from chronic overdoses. In other words, when a child under 10 overdoses, it's most likely because an adult gave it to them, not because they got into it.)
A slightly older child, say a toddler, will explore things out of curiosity, often putting things in their mouth. The main defense here is to place dangerous items in a less accessible location-- using cabinet locks, or a high shelf reachable only by adults. This only works if the medicine is always placed here-- not left on the child's bedside table. At this age, it's very difficult but not always impossible for the child to open a childproof cap. It can be counted on to slow the child down or cause them to get bored or frustrated before getting into the medicine, which gives an adult more time to realize that the medicine was left out and go put it away.
Once a child reaches a certain age, they'll be able to get into anything in the house that's not locked-- given enough time-- but on the other hand, they're old enough to understand when an adult tells them NOT to touch or take medicine. (I'm a realist, I know they won't necessarily obey, but they understand.) The main temptation here is that most over the counter children's medicine is very sweet. A child who is craving something sweet, who can get to chewable medicine more easily than, say, the sugar cubes, will go for the medicine. Unfortunately, the consequences for taking 30-40 chewable tablets may be much worse than eating a bag of M&Ms. (There are, by the way, an average of 46 M&Ms in a bag.)
Here's an idea I came up with in 5 minutes that beats childproof caps; what's yours?
Idea: Create a "medicine box" that would be basically a portable medicine cabinet. It should be easy to open for even an adult with arthritis or other dexterity problems-- if it's hard to get into, it will be left open, and that's no good. There are two main ways that it would protect children-- for houses with younger children, the box provides a second layer of security and storage, even for medicine in blister packs or boxes, and it can be moved freely to somewhere out of the child's reach. For slightly older children, it provides an easy way to instruct the child "this is the medicine box, stay out of it."