Minor injury units in Burnham-on-Sea, Chard and Shepton Mallet will see their opening hours cut for at least six months.
The NHS trust that runs them says the services have been hit by a number of frequent, short notice and unplanned closures due to ongoing staff shortages recently.
The Somerset NHS Foundation Trust says consolidating staff and restricting opening hours will ensure a 'safe and consistent' service for the county.
NHS Somerset say that the situation will be reviewed on a monthly basis during the six-month period, but it hoped the workforce position will improve by Spring 2023.
Dr Matthew Mayman, deputy chief medical officer at the trust said "Over the past few weeks, we have experienced increasing difficulties in staffing our MIUs which has led to frequent, unplanned changes to opening time in some areas.
"A combination of staff sickness, relocation, retirement, maternity leave and taking up jobs elsewhere in the NHS means that 10 of our 30 posts for the most senior clinicians within our MIUs have been vacant since the end of September - which has an impact on our ability to provide safe services without consolidating our teams and restricting the opening hours at some units.
"We want to make sure that we can provide a consistent and safe service for patients and their families. We are doing everything we can to provide consistent services at all our locations across the county to recruit and train the clinicians we need to expand the opening times at the MIUs in Burnham-on-Sea, Chard and Shepton Mallet."
What are the new opening hours?
The MIU in Burnham-on-Sea will now open Monday - Friday between 10am - 6pm. It will not provide a weekend service
The MIU in Chard will open on Monday, Tuesday, Thursday, Saturday and Sunday between 8am - 9pm. It will close on Wednesdays and Fridays when there is no X-ray service available.
The Shepton Mallet MIU will operate on Monday, Wednesday and Friday between 8am - 4pm. It will close on Tuesday, Thursday and at the weekend.
Residents who need to attend a local MIU will have to travel to Bridgwater, Frome, Minehead or Glastonbury which will continue to operate as normal - 7 days a week between 8am and 9pm.
Bernie Marden, chief officer at NHS Somerset, said: "We recognise that any changes of health and care provision can cause concern and appreciate that the amended opening hours across the MIUs in Burnham, Chard and Shepton may have an impact on some patients.
"It is vital that healthcare services in our communities not only have safe and appropriate staffing levels but also can provide consistent access to ensure patients can be cared for and treated accordingly.
"The adjustment to the opening times of these MIUS ensures that this is the case. Ensuring that the provision of this service can continue in the most appropriate way for patients.
"GP practices are also working together as primary care networks to provide evening and Saturday appointments to meet the healthcare needs of their communities. Patients can access these appointments through their usual GP surgery.”