Problems can arise when medical professionals decide to spell out exactly how they feel about their boss, workmates or their patients.
The MDDUS said that it is unlikely that any private messages posted online will stay that way and may end up in the public domain.
Dr Anthea Martin, senior medical adviser with the UK-wide MDDUS, said: ‘The two biggest mistakes that young doctors risk making when on social networking sites are breaching patient confidentiality and bringing the profession into disrepute.
‘Both could attract the attention of the GMC, which has the power to launch an investigation, suspend the doctor involved and, in the most extreme cases, remove them from the register.
‘Doctors must be scrupulously careful with their internet postings as providing information about patients, even if you do not name them, can still breach confidentiality.
‘And making derogatory or discriminatory comments about colleagues will fall foul of GMC guidelines that doctors must not make malicious or unfounded criticisms that may undermine patients' trust in their profession.'