Patients are being put at risk when they leave hospital due to reactions to their medication, a report has suggested.
Failure by surgeries and hospitals to communicate well mean patients may be given drugs without their GP knowing.
Patients may also receive drugs that interact badly with other medications, or that they are allergic to, the study by the Care Quality Commission (CQC) found.
The regulator, which visited 12 primary care trusts and 280 GP surgeries for the research, is now calling on the NHS to improve information sharing between services.
The CQC found 98% of GP surgeries provided medicines information to hospitals for non-emergency cases but not all were systematically listing previous drug reactions (24%), other illnesses a patient had (14%) or known allergies (11%).
When the CQC asked GP practices about the quality of information given by hospitals when they discharge patients, 81% said details of medicines was incomplete or inaccurate "all of the time" or "most of the time".
Almost half (47%) of doctors also complained that it took too long for hospital discharge summaries to arrive, meaning patients were seen without a full set of records.
"I would agree with the statement; working in primary care it is evident. Communication between patients, doctors and all health and health-related staff has improved considerably and is continuing to improve in relation to information on one's health, but more needs to be done between patients and those providing medical drug treatment. To improve compliance patients need to know why a particular drug is being given and its possible side effects to enable patient to make a choice. Giving a patient two days medication from a hospital and requesting a GP to continue the medication I believe is shifting the responsibility onto another health professional where he/she may not have agreed with the treatment given and is not best practice. I for one would welcome a change here in secondary care services" - V Henry, London