Ninety per cent of adults struggle to open child-proof packaging on medicines, research shows.
Many drugs are dangerous to children
Experts said this meant adults put pills and tablets into other containers which are accessible to children.
University of Sheffield researchers said packaging should be easy to open, but in a way that is too complex for young children to work out.
Campaigners said child poisoning rates have fallen in recent years but more work is needed.
Dr Belinda Winder at the Packaging Research Group in Sheffield said the main problem adults found with child-proof packaging was they did not have the physical strength to open them.
This worsened in people over 50, the journal of the Engineering and Physical Sciences Research Council reported.
Dr Winder and her team said it was "worrying" that adults therefore decided to put the medicines in easier-to-open containers which children could get into.
The solution, they said, was for child-proof packaging - or child resistant closures (CRCs) as they are known - to be based around mental abilities, not physical ones.
Dr Winder said: "CRC designs should not rely on the need for physical strength."
Instead, she said, the focus should be on having two actions which are physically undemanding but are too complicated for under fours to work out by accident.
Proposed solutions included a system where three buttons must be aligned in the correct way for the lid of a container to open.
Another suggestion was for a release button at the end of a tube which would be too long for a child's finger.
The Royal Society for the Prevention of Accidents (RoSPA) said changes to medicine packaging have already cut the numbers of children being poisoned.
David Jenkins, RoSPA's product safety adviser, said: "CRCs have been a major cause of reducing childhood accidents and fatalities for analgesics such as aspirin."
But he said many elderly people cannot get them open.
"Once they get access, or somebody opens it for them, they pour it into something else and the grandchildren get into them," Mr Jenkins said.
He added RoSPA was concerned about the issue and it welcomed the research being carried out in Sheffield.