Levothyroxine is one of the most commonly prescribed medicines in the UK
Kieran Isgin Money & Lifestyle writer
04:41, 01 Jan 2026
Levothyroxine isn’t suitable for everyone(Image: Getty Images)
The NHS has issued a warning to anyone taking levothyroxine for their thyroid condition. With approximately 33 million prescriptions dispensed annually across the UK, the medication ranks among the most frequently prescribed by the NHS.
It is primarily used to treat an underactive thyroid gland, also known as hypothyroidism. Generally, it will be prescribed either as a tablet or liquid form for the patient to swallow, based on what the GP deems most appropriate.
Whilst levothyroxine proves effective in treating an underactive thyroid in most instances, the NHS has cautioned that certain individuals should not be prescribed it. This can be due to various reasons, including the medication potentially increasing the risk of complications from other health conditions.
The NHS website states: “Levothyroxine can be taken by most adults and children. However, it’s not suitable for some people.”
People who may not be able to take levothyroxine
According to NHS guidance, you may not be able to take levothyroxine if one of the following applies:
- You have a heart problem, including angina, heart disease or heart failure
- You have a health problem that affects your adrenal glands
- You have previously had a heart attack
- You have an overactive thyroid that produces too much thyroid hormone (thyrotoxicosis)
- You have diabetes
- You have previously had an allergic reaction to levothyroxine or any other medicine
- You have high blood pressure
When to call 999
Levothyroxine can cause a wide array of side effects, some of which may warrant a call to 999 or a visit to A&E. Common side effects of levothyroxine include:
- Flushing or sweating
- Feeling restless or excitable
- Trouble sleeping
- Nausea
- Headaches
- Vomiting
- Shaking
- Diarrhoea
- Muscle cramps
Bear in mind that there may be additional side effects associated with levothyroxine not listed above. For comprehensive details on side effects you may encounter while taking the drug, you should read the leaflet inside the packet that came with your medicine.
While these common side effects may be discomforting, they are typically not serious and will not require an emergency hospital visit. However, if you do experience them and they persist, the NHS recommends that you consult a doctor or pharmacist who can provide further professional assistance.
However, if you experience a rapid or irregular heartbeat, then it is advised that you either speak to a doctor or dial 111 as soon as possible. Moreover, if you experience any chest pains while taking levothyroxine, it is recommended that you dial 999.
Full details on levothyroxine and its side effects can be found on the NHS website here.