Does cortisone cause weight gain, and is cortisol involved? What do the studies say, and what should you do in practice?

It is one of the most common concerns for people who find themselves having to take a cortisone-based treatment and which, at times, leads them to miss doses or stop the treatment on their own, with potentially serious risks. But what do the studies actually say? And what role does cortisol play – the stress hormone that has taken centre stage in much of the content on social media in recent months, often cited as the cause of bloating or difficulty losing weight? Let’s try to clarify the situation, distinguishing between the medication and the natural hormone.

It depends mainly on the duration of treatment. A systematic review analysing 21 studies of people taking oral corticosteroids found that, in short-term treatments, weight gain was minimal or non-existent; in long-term treatments, however, it can become clinically significant. In other words: a course of treatment lasting just a few days for acute inflammation is unlikely to cause a significant increase in weight; the risk increases when treatment lasts for weeks or months. At high doses and over long periods, cortisone can in fact increase appetite, promote fluid retention and redistribute body fat towards the abdomen, face and back of the neck: the so-called ‘moon face’. A review that pooled data from 118 randomised controlled trials, involving a total of over 17,000 participants (of whom more than 8,500 were treated with corticosteroids), confirmed an increased risk of weight gain, as well as higher blood pressure, blood glucose levels and worse cholesterol and triglyceride levels, in treated patients compared with controls.

Cortisol is a hormone produced by the adrenal glands, which the body uses every day for essential functions: it regulates the metabolism of sugars, fats and proteins, helps control blood pressure, modulates the immune system and maintains the body’s energy balance. To refer to it simply as the ‘stress hormone’ is an oversimplification: the stress response is one of its functions, not the primary one in everyday life. Its production also follows a precise 24-hour rhythm, peaking upon waking and gradually declining until night-time. A temporary rise in cortisol in response to a stressful situation is therefore not a problem: it is a normal adaptive mechanism.

Because both the concept and its measurement are being misused. Online, there is a tendency to attribute common and non-specific symptoms – fatigue, bloating, difficulty losing weight – to ‘high cortisol’, when in the vast majority of cases these symptoms have entirely different causes. And people talk about ‘high cortisol’ almost always without measuring it properly: as it is a hormone with a distinct circadian rhythm, a single reading taken at any point during the day – as in the tests sold online – does not provide any reliable information. Even when it comes to body weight, the data do not support the narrative circulating on social media: a systematic review of 13 studies on calorie restriction and cortisol found no association between changes in cortisol levels during a diet and the actual weight lost, and a meta-analysis of over 1,500 adults found no correlation between BMI and cortisol levels in blood or urine.

From a medical point of view, the cause for concern is a chronic and pathological excess of cortisol: Cushing’s syndrome, caused by prolonged use of corticosteroid medication or, more rarely, by a tumour – almost always benign – of the pituitary gland or the adrenal glands. It is a potentially serious but rare condition, which is not limited to weight gain: it also involves loss of muscle mass, altered fat metabolism with fat deposition mainly on the trunk and face, increased hunger and reduced energy expenditure. Here too, however, the diagnosis is not based on a single symptom or a random cortisol reading, but on specific tests – overnight salivary cortisol, free cortisol in a 24-hour urine sample, a dexamethasone suppression test – which are only requested where there is a concrete clinical suspicion, after ruling out the use of corticosteroid medication.