Some patients are reluctant to talk to health professionals
Poor communication is most often to blame for people ending up in hospital due to "medication errors", UK researchers say.
Limited access to the patient's medical notes was also found to contribute to mistakes over medicines.
The study, published in Quality and Safety in Healthcare, found some patients may also not be told enough information about their prescription.
It is estimated one in 15 hospital admissions are due to drug errors.
A team of researchers at the University of Reading looked in detail at 18 cases of patients in Nottingham who ended up in hospital due to a drug prescribed by a GP.
Some patients had been prescribed drugs to which they had an adverse reaction, some not prescribed drugs they should have been and others not monitored properly.
Interviews with 62 GPs, pharmacists, practice nurses and patients showed failure of clinicians to communicate between themselves and with to patients were the main reason for the medication errors.
Better liaison could have prevented many cases regardless of whether the problem was related to prescribing, monitoring or patient adherence to the medication.
The researchers also found that some patients are reluctant to ask health professionals about their medicine.
And in some cases pharmacists automatically assumed the patient had been given information about their medicine by the GP.
GPs working out of hours and pharmacists did not always have access to patient records which also led to prescribing and monitoring mistakes.
Study leader, Dr Rachel Howard, a researcher at the University of Reading, said the problems leading to drug errors were complex and there was no one solution.
"Technical solutions such as computerised assisted prescribing and the NHS patient care record are unlikely to be sufficient on their own to improve the situation.
Co-author, Professor Tony Avery, from the University of Nottingham, said there were a couple of examples where the patient just had not heard what the doctor said and was afraid to ask.
"Simple communication is very important - even basic things like checking understanding."
Professor Aziz Sheikh, an expert in medication errors at the University of Edinburgh, said drug errors leading to hospital admission was a big problem and not just in the UK.
"In the main, these admissions are preventable and this research is looking in more detail at where the problems are.
"Certainly communication is very important."
He added it would be interesting to see whether the electronic patient record would prevent more errors once it was in place as any clinician treating the patient would be able to see relevant medication information, whatever their location or the time of day.
"In theory it should make a substantial difference," he said.
A spokesman for the National Patient Safety Agency said they recognised that poor communication can often be the cause of preventable drug-related hospital admissions.
"Whilst technology and improved IT systems may reduce the prevalence of these errors in the long term, it is important that communication both between healthcare professionals and between patients and practitioners is addressed as an issue immediately," he said.