My uncle has recently suffered a lot of pain at the hands of doctors. Doctors had been busy treating the main disease of course, but the complications from treatment / medicine - were not studied carefully by them. It prompted me to scrawl the web for the mistakes that doctors do, and just keep myself updated. Sharing my piece of information with you -

1) Oops Surgeon left some object inside the body : Yeah - the funny it sounds - the dangerous it is. Doctors from all over the world - tend to forget some object in the person they operate. The top reasons for this mistake are emergency operations, fatigued surgeon, or sudden last minute change in operation procedure.

2) Cosmetic Goof ups : This mistake has come second in my research. May docs have given improper botox injection dosages; or cheaper breast implants. Liposuction's done in cheaper / ill-equipped clinics lead to fluid overdose in body; leading to serious long-term heart-lung complications. Best to follow the cosmetic surgeries with a known appropriate respectable hospital, with proper appointment.

3) Cut / operated on wrong body part : Now that's the worst nightmare for any individual. Its like horror movie playing in real life for the person. Hospitals report such errors as "wrong-site adverse events". One such event in Britain occurred in 2002 when doctors removed wrong kidney; and patient died on the operation table. Such problems are beyond the individual's control.

4) Improper Anaesthesia : Imagine a patient waking up on the OT table, not able to cry or say anything, looking at himself open / cut. That's like "Living Dead".

5) Improper Dosage : there are international norms about the proper dosages to be given by doctors to patients. However, some doctors - would simply just go by their standard form, ask basic questions to patient and prescribe the medicine - without asking if patient is allergic to that medicine, or without analyzing whether the drug has a negative reaction - which in turn is allergic to the patient.
That was the problem my uncle was facing. Bigger worry - the doctor just didn't consult another doctor who was expert in the field of that allergy. When doctors dont communicate to each other - how are we expected to get a healthy world & safe!!

6) Endless Tests : Changing the doctors often results in just one thing for a patient - more tests to be done; or same tests to be repeated by the new doctor - because "some hours have passed". A certain amounts of tests are required....but when you have the test results; and you know the disease cause - better cure it instead of asking for more / repeat tests. There has to be some break-even in the tests and the cures.
This mistake, though not accepted by doctors / physicians... are often reported by patients. Docs - better wake up

7) Post operative infections : Do the doctors keep mum these days on post - operative infections; or do they don't know at all? The infections spread most out of the ill-managed hospitals

8) Drug dependency : this kind of mistake is very rare to happen; and it does happen only with improper followup by the patient. Regular prolonged use of same drug over a consistent period makes body non-responsive to the drug sometimes. Because of that - if the body needs the drug in future, the effectiveness decreases.
Doctors too often prescribe a pain killer, or a anti-depressant or anti-anxiety medicine for common ailments - just to make patient feel better. They start interfering with the body's own pain relieving system.

Most doctors don't listen. Study shows that more than 90% doctors interrupt patients within first 20 seconds of communication.
Also, the doctors need to realize the patient is no-toy : and that a life is on the table - so better plan first properly and completely with the team before entering the operation theater.