Health boards across Scotland have been dealing with a surge in falls and fractures due to icy weather, and the doubling of flu rates in December compared to last year.
Increased demand has led to more people waiting longer to be seen at A&E over the festive period.
Meanwhile, ministers have praised staff for going “the extra mile” to ensure patient safety.
The British Medical Association (BMA) in Scotland said the situation should not be dismissed as “the inevitable increase in pressure that winter brings”.
BMA Scotland chair Dr Peter Bennie said: “We have seen staff in NHS Scotland working incredibly hard, in extremely difficult circumstances over recent days, to deliver the care that people need.
“I’d like to add my gratitude to the many expressions of thanks that teams working across the country have received.
“But, to be honest, it is not thanks that doctors and their colleagues want. Instead of gratitude, we need a long term, sustainable plan that closes the growing gap between resources - in particular, finances - and the demand for services.
“And we must not simply dismiss this as the inevitable increase in pressure that winter brings.”
Dr Bennie said multiple targets, an ageing population and a gap in funding were stretching the system and the workforce “beyond their means”.
He said: “In winter, that results in the type of rapid deterioration of services that we have seen over recent days.
“But over the course of the rest of the year it also means the ongoing eroding of standards, care and services.”
The organisation has called for more effective funding, less focus on targets and action on healthcare staff vacancies.
Dr Bennie added: “If we don’t take this kind of action, we risk not only another hugely challenging winter period next year, but an NHS simply unable to cope with huge demands being placed on it.”
Health Secretary Shona Robison said: “Health Boards have worked to put in place robust winter contingency planning arrangements, which they’ve demonstrated in their response to exceptional winter pressures.
“Staff right across Scotland should be thanked for their hard work and dedication throughout this time.”
She added: “We have record staffing in Scotland’s NHS and we’re aiming to go further.
“This is supported by record high investment, that is increasing by £2 billion by the end of this parliament.
“Having the right measures on the performance of our NHS and care systems is vital.
“That’s why we welcome Prof Sir Harry Burns’ recent report on targets and indicators, and the principles he outlines, which we will now use to underpin further work to develop better ways of understanding people’s wider experience of care.”
Scottish Labour health spokesman Anas Sarwar said the NHS was facing a “serious staffing crisis”.
“While the SNP accepts that demographic changes are impacting services, the government continues to shirk responsibility for previously cutting medical and nursing training places, a decision which has resulted in vast numbers of unfilled posts.
“Over the last month we have seen office staff having to volunteer to help GPs and hospital staff to cope with the demand. That is utterly unacceptable in the 21st Century NHS.”