What are some causes of sudden weight gain?

It’s common to gain or lose a few extra pounds. But what if you notice sudden weight gain and are unsure what’s causing it? There may be a simple explanation for sudden weight gain, or it may take a deeper dive to figure out the cause. 

If you notice you’ve suddenly gained several pounds over the course of a few days to a week and haven’t changed anything like your diet, exercise, water intake, etc., there could be something else going on. Similarly, it may warrant a visit to your healthcare provider if you find that you’re consistently gaining week after week without making changes to your lifestyle. 

Your weight can fluctuate for many reasons, including water intake, inactivity, dietary changes, menstrual cycles, menopause, aging, and more. So, if you notice that the scale number is a bit higher after a night of eating salty foods (causing your body to retain water), there’s no need to panic. 

That said, rapid, unintentional weight gain may be due to a variety of health conditions or may be a side effect of certain medical treatments. Let’s look at a few of these causes more closely. 

Medications

Some medications may cause you to gain a few pounds. Others have been linked to increases of up to 10% or more of your initial body weight. Drugs most commonly linked to more dramatic weight gain include (Verhaegen, 2019; Wharton, 2018):

• Antipsychotics

• Blood pressure medications

• Mood stabilizers

• Anticonvulsants

• Antidepressants

• Insulin (used to treat diabetes)

• Corticosteroids 

The reasons why these medications cause weight gain vary. Some drugs can make you hungry, causing you to eat more. Others can make you retain water or change your metabolism (Verhaegen, 2019).

If you suspect a medication is causing weight gain, don’t stop taking it without first talking to your healthcare provider, as stopping some medications can be dangerous. There may be alternative or additional medications that can help. In some cases, tapering your dose (versus stopping cold turkey) may be required before you transition to a new drug (Wharton, 2018).

Hypothyroidism

If your body is not making enough thyroid hormone—a condition called hypothyroidism—it can make you feel tired, weak, and cold. An underactive thyroid causes your metabolism to slow down, making it easier to gain weight. It can also contribute to water retention which doesn’t help the numbers on the scale (Sanyal, 2016; Laurberg, 2012).

Oral thyroid hormone replacement may reverse symptoms and help return your metabolism to normal. This requires a consult with your healthcare provider who can check your thyroid levels and discuss a treatment plan (Sanyal, 2016). 

Diabetes and prediabetes

After you eat, the hormone insulin helps send glucose (blood sugar) into your cells where it’s used for energy. In the case of insulin resistance, your cells don’t take up the glucose as they should, leading to too much sugar in your bloodstream. This excess blood sugar is then stored in your body tissues as fat. 

Research shows weight gain increases the risk of insulin resistance. However, insulin resistance can also make it easier to gain excess weight and can lead to prediabetes and type 2 diabetes (Howard, 2004; Freeman, 2021). Taking insulin can also increase the risk of weight gain (as noted above when we discussed medication side effects).

Talk to your healthcare provider about your potential risk factors for prediabetes or diabetes. Lifestyle changes, such as reaching and maintaining healthy weight through a healthy diet and regular exercise, may help prevent or even reverse these conditions. 

Polycystic ovary syndrome

Polycystic ovary syndrome (PCOS)—a hormonal imbalance in women—can make it easier to gain weight (often around the waist) and harder to lose it. The condition causes cysts on the ovaries and can lead to irregular periods, extra body hair, and acne. Up to 90% of women with PCOS may have insulin resistance (Glueck, 2018; Barber, 2019). 

Treatment usually includes exercise, a healthy diet, and sometimes medications that can help with ovulation and reduce hair growth and acne outbreaks (Barber, 2019). 

Cushing’s syndrome 

Gaining weight around the waist, face, upper back, and neck may be the result of Cushing’s syndrome. This condition is often linked to medications like long-term corticosteroids use for chronic medical conditions (Chaudhry, 2022). 

It can also occur when your pituitary gland tells your adrenal gland to make too much cortisol. Cortisol, typically released in response to stress, increases blood sugar to give you more energy to deal with the stressor. However, too much cortisol can work against insulin, eventually leading to insulin resistance (Chaudhry, 2022). 

If a medication is causing Cushing’s syndrome, your healthcare provider may be able to switch to another drug. In other cases, surgery may be needed to remove a pituitary tumor that is triggering cortisol release (Chaudhry, 2022). 

Stress and depression

Stress boosts the hormone cortisol. As we discussed above, high cortisol levels are linked to insulin resistance. Psychological stress can also cause fat to accumulate around the waist and increased cravings for calorie-dense foods in some people. People with depression may also notice weight gain (Scott, 2012; Sutin, 2012). 

If you’re experiencing depression, stress, or any type of mental health issue, your healthcare provider can help you explore possible solutions. For example, stress management may help reverse weight gain. In a small study, those who took part in relaxation techniques like deep breathing lost more weight than those who received only diet advice (Xenaki, 2018).

Insomnia

A lack of sleep not only makes you feel tired, but might also change your metabolism and boost your appetite. When you don’t get enough sleep, levels of ghrelin—a hormone that tells your body to eat—increase. At the same time, leptin—a hormone that signals that you’re full— decreases.  

Research shows a lack of sleep may make you more likely to eat sugary foods and that it can change your metabolism—making it harder to control blood sugar. Some data suggests a chronic lack of sleep may be linked to an increased risk of type 2 diabetes (Mosavat, 2021; Al Khatib, 2018).

If you’re having sleep troubles, it’s important to talk with your healthcare provider. Sometimes sleep studies can help identify underlying causes, such as obstructive sleep apnea.

Quitting smoking

Quitting smoking can dramatically improve health and reduce the risk of lung cancer. Unfortunately, it may also cause you to gain weight. Many people gain 2–10 pounds over the first year after quitting smoking (Aubin, 2012). 

Nicotine is an appetite suppressant that can also speed up metabolism. For some, the stress linked with quitting can lead to increased eating. For others, foods high in sugar and fat taste better after quitting smoking, leading to eating more and weight gain. That said, research shows that around 16% of people lost weight in the first year after quitting (Bush, 2016; Aubin, 2012). 

If you’ve just quit smoking and are concerned about weight gain, your healthcare provider can offer options. Some people use nicotine replacements—in the form of a patch, gum, nasal spray or inhaler—to help with the transition.

Edema (fluid retention)

Swelling caused by a build-up of fluid in your body can cause unexplained weight gain. Often called water weight, edema can be minor and caused by salt, inactivity, medications, or surgery. 

However, the build-up of large amounts of fluid can be a symptom of certain medical conditions, like kidney disease, heart failure, and blood clots. For example, some people with heart failure may notice up to a 5-pound weight gain over a week or two from fluid buildup (Howie-Esquivel, 2019; Lent-Schochet, 2022). 

This is why it’s important to talk to your healthcare provider about sudden increases in weight. In cases of edema, your healthcare provider will tailor treatments to address the underlying medical issue. 

If you’ve assessed your lifestyle and don’t seem to be making many changes, yet are noticing sudden or progressive weight gain, it’s best to contact a healthcare provider who knows your medical history. 

Your rapid weight gain may be due to a medical condition. But it may also be due to unknowingly overeating or eating the wrong types of foods, in which case, a nutritionist or dietitian can help you build a meal plan that suits your dietary needs. Either way, getting to the bottom of rapid, unexplained weight gain can help lead to solutions. 

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

Current version

July 01, 2022

Written by

Kristin DeJohn

Fact checked by

Chimene Richa, MD

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About the medical reviewer

Chimene Richa, MD

Dr. Richa is a board-certified Ophthalmologist and medical writer for Ro.