Almost one in five people say they have taken prescription medicines wrongly, a survey has suggested.
The poll of almost 2,000 people for Lloydspharmacy found many misread labels - and take the wrong dose or take drugs at the wrong time.
One man whose asthma was triggered by his cat sprayed the animal with the inhaler, as a "cure" for his symptoms.
The poll comes as NHS data showed the number of prescriptions written in 2007 in England was double the 1997 figure.
The NHS Information Centre data showed around 796 million prescriptions were written last year, up 59% from 1997.
And two thirds of prescriptions are now provided to people over 60.
On average, people in that group received 42.4 items per head last year, compared to 22.3 items in 1997.
'He didn't take the cap off'
Andy Murdock, pharmacy director for Lloydspharmacy, said: "We know that many patients choose not to complete their course of medication, but this study reveals a different type of problem - patients who, for whatever reason, take their medicines incorrectly.
|Our pharmacists have reported many instances where patients have been confused by their medicines
Andy Murdock, Lloydspharmacy
He said the biggest problems were seen among older people who are taking a number of medicines.
Mr Murdoch said: "Our pharmacists have reported many instances where patients have been confused by their medicines.
"One patient set out a range of medicines and described the frequency and dosage for each.
"It turns out that for several months she had been taking a sleeping pill first thing in the morning."
He added: "Another patient reported difficulty using his asthma inhaler.
"When the pharmacist asked him to demonstrate, the problem became clear; he wasn't removing the cap."
People who are taking a range of medicines or who have been taking a drug for a long time may be offered a free medicines use review (MUR), designed to check they are taking their medicines properly and that they are still having the necessary effect.
MURs were introduced four years ago as part of a revised pharmacy contract. They are offered by pharmacists including Lloydspharmacy.
|It is vital that patients are given the information they need to get the best results from their medication
Professor Steve Field, Royal College of GPs
People with long-term conditions may respond differently to medicines they've been on for some time. An MUR will pick this up.
Lloydspharmacy said 55% of its 500,000 MURs have resulted in a recommendation from the pharmacist that the patient change their medicine taking routine in some way.
A further 25% resulted in a GP referral which, in many cases, led to the patient switching medications or ending treatment altogether.
Professor Steve Field, chairman of the Royal College of GPs, said: We are concerned at the staggeringly high numbers quoted in the survey.
"It is vital that patients are given the information they need to get the best results from their medication.
Professor David Cousins, the National Patient Safety Agency's head of pharmacy, said it was crucial pharmacists discussed medication with the patient or their carer every time they issued a prescription.