The blame for being overweight can normally be placed on the simple equation that we are consuming more calories than we are burning off, through a combination of eating too much of the wrong foods and not exercising enough; and that we can only achieve a healthy weight with a balanced, healthy diet and active lifestyle.

However, in some instances weight gain can at least partly be attributed to already existing health problems, or the medication we take to treat it.

Here we’ll discuss in some detail those conditions where weight gain may be a related symptom.

  1. Hypothyroidism
  2. Polycystic ovary syndrome
  3. Depression and anxiety
  4. Fluid retention
  5. Cushing's syndrome


Hypothyroidism, also known as thyroid hormone deficiency, is a condition caused by low levels of the hormones produced by the thyroid gland, which are used to manage the body’s metabolism. More common in women than men, the symptoms can often take years to develop and can be associated with weight gain in many people.

It is not to be confused with hyperthyroidism, which is caused by overactive production of hormones by the thyroid gland.

The thyroid gland is a butterfly shaped, ductless gland situated just below the Adam’s apple in the throat. The thyroid releases the hormone thyroxine (alternatively known as T4), most of which is transformed into the hormone triiodothyronine (T3) by the body’s organs, such as the kidneys and the liver.

These hormones manage the body’s metabolism; the chemical reactions that break down molecules in food and convert it into energy. This essential process enables muscle growth and development, keeps our organs and functions working properly and helps to repair the body when damaged.

Hypothyroidism occurs when the thyroid gland cannot produce enough thyroxine to manage metabolism properly, causing the body to become ‘run down’.

This process can occur over a long period of up to several years, so you may not notice these symptoms at first, but you may sense them worsening over time.

Symptoms will be slightly different for each person affected, but commonly include:

  • Weight gain
  • Fatigue
  • Heightened sensitivity to the cold
  • Depression
  • Feeling constipated
  • Disruption to the menstrual cycle
  • Feeling less mentally alert
  • Dry hair and skin
  • General aches and stiffness in the muscles and joints

If the condition is left untreated, it can lead to heart disease, problems with fertility, mental health issues and nerve damage.

The decrease in hormone production is usually attributed to damage sustained by the thyroid gland. In many cases it is attacked by the body’s own immune system through autoimmune thyroiditis, the most common of which is known as Hashimoto's disease. This can cause the gland to become swollen, leading to a lump in the throat known as a goiter. If untreated, the goiter can increase in size, become unsightly and make breathing and swallowing difficult.

Hypothyroidism can also be caused by earlier surgery or treatments for an overactive thyroid gland (hyperthyroidism) or cancer of the thyroid. Medication, most commonly lithium, but also interferon and amiodarone, can lead to the development of the condition.

Some viral infections can cause short term damage to the thyroid gland, and around one in 3,500 to 4,000 babies are born with congenital hypothyroidism according to the British Thyroid Foundation.

You are more susceptible to the condition if someone in your family has had hypothyroidism, or you have a history of autoimmune diseases.

If you think you have an underactive thyroid, you should see your doctor, who may want to test your blood for hormone levels. If you are found to have hypothyroidism, you will be prescribed a hormone replacement treatment, which is generally a tablet containing the ingredient levothyroxine. You may need to take this medication for the rest of your life.

These tablets supplement the levels of thyroxine and work to return your body’s metabolism to its normal level. It may take quite some time for your doctor to find the right dosage for you, and it can take up to several months for you to notice any improvement. You will also regular regular blood tests to check your hormone levels.

Weight gain is a well known side effect of hypothyroidism. However, the amount of weight gain directly caused by the condition is relatively modest, usually amounting to around 5 to 10 pounds, and rarely more than 20 pounds, most of which is salt and water.

Upon successful treatment, an average patient can lose up to 10% of their body weight, but according to the American Thyroid Association, the amount lost can be insignificant if the condition has developed over a long period of time.

If you have gained weight, but are not showing any other symptoms of hyperthyroidism, it is unlikely that you have the condition. Similarly, if you are being treated successfully for hyperthyroidism, but are still overweight, this will most likely be caused by other factors as you will be able to gain and lose weight in the same way as someone without the condition.


PCOS, which stands for Polycystic Ovary Syndrome, is thought to affect up to one in five women in the United Kingdom. Many don’t experience any symptoms, but in cases where they do, they tend to manifest themselves in women during their late teens or early 20s.

The condition is thought to be linked to a resistance to the hormone insulin and disproportionate levels of androgens (male sex hormones which are also present in women).

PCOS occurs when the development of eggs in the ovaries are hampered by high levels of testosterone. The follicles where the eggs are produced are not able to release them for ovulation.

This causes irregular periods and problems with fertility, and other symptoms include excess hair growth or hair loss and acne.

High levels of insulin present in the body lead to difficulties with turning glucose into energy, causing weight gain. It can become a vicious circle, as the extra weight in turn encourages the body to produce even more insulin.

The androgens present in women also cause extra weight gained to sit around the waist, which increases the risk of problems such as heart disease and type 2 diabetes.

There is no cure for PCOS, but it can be managed with lifestyle changes, medication or a combination of both. Losing weight with exercise and adjustments to your diet can greatly improve your condition, with a loss of just five per cent of your total body weight showing noticeable results.

You may also be prescribed statins or weight loss medication, and the use of fertility treatments can enable the majority of women with PCOS to have children.

Depression and anxiety

One in four of us are affected by a mental health issue each year. While many people experiencing depression and anxiety actually lose weight, the symptoms can cause others to put weight on. Both can have serious health implications.

Disturbed sleep patterns, a lack of energy or motivation and feeling hopeless can cause those affected to avoid physical or outdoor activities and eat fatty and sugary foods for comfort. When someone puts weight on, they can further lose self-confidence or feelings of self-worth, and the cycle of poor diet and weight gain continues.

There are many measures someone can take to help improve their mental well being. In addition to consulting with a doctor about medication, talking therapies, mindfulness and exercise can help too. Spending time with friends and family, trying a new hobby or meeting with a group of people who share the same interests can also be extremely helpful.

Fluid retention

Medically referred to as oedema, this accumulation of fluid under the surface of the skin between areas of tissue or in one of the body’s organs is extremely common, especially in the feet and lower legs. While in some cases it can simply be a short term symptom of standing up all day, it can also be a signifier of a more serious medical condition.

Weight gain is just one of the symptoms of oedema, with soreness of the muscles, joints and limbs, and changes in the colour of the skin being among others. The condition known as pitting oedema leaves an indentation after applying pressure to the affected area.

Oedema can be a symptom of pregnancy, or a disease of one of the internal organs, such as the heart, liver or kidneys. It is also a side effect of oral contraceptives, corticosteroids and medicine for high blood pressure.

The symptoms of fluid retention often clear up on their own, but if they persist you should see you doctor to check that it is not part of an underlying health issue. They may prescribe medication and also suggest some lifestyle changes such as changing your diet or taking more exercise.

Cushing’s syndrome

A rare condition, Cushing’s syndrome is caused by a surplus of the cortisol hormone. It is usually caused by prolonged exposure to corticosteroid medicine but may also originate from the growth of a tumour in the pituitary gland, which can be called either endogenous Cushing’s syndrome or Cushing’s disease.

The weight gain associated with Cushing’s syndrome affects the face as well as the middle section of the body. Fat also builds in the area between the shoulders and the back of the neck, forming a ‘hump’. People with the condition can develop fragile skin, which allows it to bruise easily, become discoloured and show stretch marks. They can also have high blood pressure, brittle bones, problems with fertility and depression.

Determining whether or not you have Cushing’s syndrome can be a long process, as your symptoms may surface gradually, and they can be similar to those associated with hypothyroidism or high blood pressure. If you are diagnosed, your doctor will manage your dosage of corticosteroids or issue you with medicine to inhibit the effects of cortisol.

If you are found to have endogenous Cushing’s syndrome, you may be admitted to surgery to remove the tumour from your pituitary gland.

Talking to your doctor

If you’ve become concerned about your weight, you should make an appointment to see your doctor. They will be able to talk to you about how it can be influenced by other underlying health issues and if they affect you.

Not only will they be able to help with medication if required, they may also be able to help you implement lifestyle changes which can improve your overall health and help you lose weight where necessary.

Page last reviewed:  01/10/2020