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What causes rapid weight gain? Related conditions and treatments

Rapid weight gain can be caused by various factors such as medications, hormone fluctuations, and lifestyle changes
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By | Apr. 17, 2025 Medically reviewed by Leslie Greenberg, MD
Scale: What causes rapid weight gain?

Key takeaways

  • Rapid weight gain is a common symptom that may be caused by changes in diet, certain medications, fluid retention, hormone fluctuations, and other conditions.

  • Rapid weight gain typically requires immediate medical attention if it’s accompanied by symptoms like swelling, seizures, vomiting, severe headaches, trouble breathing, or an increased heart rate.

  • Rapid weight gain generally requires evaluation and treatment since it may indicate an underlying condition. It typically resolves after the underlying condition is treated.

  • The treatment of rapid weight gain depends entirely on the cause but may include diet, exercise, counseling, weight loss drugs, or discontinuing certain medications. Read more about treatments for thyroid issues, PCOS, chronic kidney disease, and heart failure.

  • Use coupons for weight gain treatments, like Adipex (phentermine), Saxenda (liraglutide), Contrave (naltrexone/bupropion), and Wegovy (semaglutide) to save up to 80%.

In this article:

Overview: What does rapid weight gain look like?

So, the numbers on the scale took a recent jump. Most people will experience some type of weight gain over their lifetime—and smaller weight fluctuations are very common—but it can be slightly more alarming when the pounds start to add up quickly. There’s no overarching clinical definition, although a noticeable increase in body weight over a few days or weeks is typically cause for alarm and further investigation. 

This additional body weight can show up in various places, including the abdomen, thighs, buttocks, upper body, hands, and ankles. It all depends on the specific cause and the location on the body that you routinely gain weight in first. Besides changes in weight, symptoms can include fatigue, lethargy, bloating/swelling, shortness of breath, constipation, and vision issues.

What causes rapid weight gain?

It might be easy to detect the symptoms of sudden weight gain, but it can be hard to pinpoint the cause. That’s because it can stem from numerous sources, like lifestyle changes, dietary influences, medications, medical conditions, or some combination thereof. That said, here are several of the most common reasons for weight gain.

Certain medications

While medications can have amazing benefits, some may cause weight gain as a side effect. These drugs include:

  • Antidepressants: Some antidepressant drugs can increase appetite, causing the patient to eat more. Studies have shown that this effect in common antidepressants like Prozac and Lexapro can lead to weight gain. Conversely, some individuals, when depressed, eat less, and when their mood gets better, they eat more. 
  • Corticosteroids: Medications like prednisone may affect the body’s metabolism and how it stores fats and water. In one 2015 study, over 22% of patients treated with prednisone gained more than 10 kg. Prednisone may also cause patients to have an insatiable desire to eat. 
  • Antipsychotics: According to research, these drugs may affect glucose metabolism, increase cholesterol and triglyceride levels, and contribute to hypertension, which can lead to metabolic syndrome.
  • Antihyperglycemics: These diabetes drugs increase insulin levels and appetite and affect fluid and fat retention. So common diabetes drugs like insulin, sulfonylureas, and thiazolidinediones may cause weight gain.
  • Antihypertensives: Blood pressure medications, specifically beta blockers, might influence the body’s metabolism, which may cause an increase in weight. Beta blockers also decrease the heart rate, causing some patients to feel sluggish and exert (or exercise) less. 

Anyone who experiences rapid weight gain after taking one of these drugs should consult their doctor, who might adjust the dose, discontinue the medication, or find a suitable alternative.

Hypothyroidism

The thyroid is an endocrine gland in the neck that produces hormones responsible for energy consumption (metabolism) and organ functions. When an underactive thyroid doesn’t produce enough hormones, the body converts fewer calories to energy. Sometimes, this change is temporary and short-term. But sustained decreases in thyroid hormones is called hypothyroidism, and it can lead to weight gain. According to the American Thyroid Association, people with hypothyroidism can often attribute 5–10 pounds of weight gain to the condition.

“Some subtle signs that this may cause your rapid weight gain include sensitivity to cold, dry skin, hoarseness, fatigue, constipation, and muscle weakness,” says Trista Best, RDN, LD, registered dietitian at The Candida Diet.

Polycystic Ovarian Syndrome (PCOS)

PCOS is characterized by elevated levels of androgens (male hormones) in women, and potentially estrogen, too. This imbalance often causes irregular menstrual cycles, abnormal hair growth, thinning hair, acne, and ovarian cysts. It can also increase insulin resistance, changing how the body processes glucose. When the body experiences elevated blood sugar levels, it may store the glucose as body fat instead, leading to excess weight.

According to Best, symptoms that might indicate PCOS “may be the cause of your rapid weight gain, include irregular periods, excessive hair growth, and oily skin or acne.” Women experiencing these symptoms should see a doctor for an exam.

Chronic stress

When an individual experiences a stressful situation, their body kicks into fight-or-flight mode, which includes the release of a hormone called cortisol. It triggers the body’s survival processes while slowing down all the functions not necessary for immediate reactions. So, while it increases blood pressure and insulin production, it decreases metabolism. Occasional cortisol spikes might not contribute to rapid weight gain, but studies have found links between long-term cortisol increases and obesity.

Cushing’s syndrome

This is when the body produces too much of the stress hormone cortisol. As outlined above, chronically elevated cortisol can affect blood pressure, insulin, and metabolism, causing weight gain. Cushing’s syndrome may stem from pituitary tumors, adrenal tumors, ectopic tumors, or long-term use of glucocorticoids. Some common treatments include surgery, radiation therapy, or discontinuation of medications, depending on the underlying cause.

Heart or kidney issues

Weight changes from either of these conditions stem from fluid retention. During heart failure, the heart can’t pump blood effectively enough, so the body begins storing fluid elsewhere, causing swelling and potentially weight gain. Similarly, the kidneys are responsible for removing excess water from the body, so when they aren’t functioning well, they may also cause fluid retention and weight gain.

Research suggests that weight changes are common in people with moderate-to-severe chronic kidney disease. At the same time, the American Heart Association says anyone who gains 2–3 lbs over 24 hours, or 5 lbs in a week, should see a doctor.

Lack of sleep

According to a 2022 study, an increase in sleep duration can correlate with decreased caloric intake. Not only does adequate sleep help regulate appetite, but it can reduce or eliminate those midnight fridge runs. Unfortunately, that means people who have conditions that affect sleep, like insomnia or sleep apnea, may experience weight gain. Treating these underlying conditions, sticking to a consistent sleep schedule, and getting 8+ hours of sleep per night are all parts of a comprehensive weight loss plan.

Poor diet

This is probably the most common and obvious cause of weight gain. A 2023 study found that those who ate more processed carbohydrates like sugars, starches, and refined grains were more likely to gain weight, while people who increased consumption of whole grains and non-starchy vegetables were not. While weight gain from a poor diet is typically slower, these unhealthy eating habits can exacerbate rapid weight gain from medications or underlying conditions. On the flip side, a healthy, well-balanced diet may help mitigate some of the weight gain from other sources.

Sedentary lifestyle

Besides diet, exercise is probably the most well-known weight-loss tactic. So, while regular physical activity can help manage weight, a lack of exercise can do the opposite. Much like diet, a sedentary lifestyle will typically cause slower weight gain than medication conditions or medications, but it can contribute to gains from other causes. A study from 2022 showed that prolonged daily sitting was associated with higher body fat percentages, so getting on a regular workout plan might help control the weight gain from some of the causes listed above.

Should I be worried about rapid weight gain?

“Patients have the right to be counseled when weight gain or loss is sudden, especially when it is associated with dangerous symptoms like swelling or shortness of breath,” says Dr. Michael Chichak, MD, Medical Director at MEDvidi. “It is vital to pinpoint which medical condition needs immediate medical attention.” Other concerning symptoms that might require medical attention when accompanying rapid weight gain include constipation, hair loss, feeling cold, swollen feet, vision changes, palpitations, tremors, and sweating.

People who have pre-existing medical conditions—particularly cardiovascular issues—might need to monitor their weight gain more closely. According to the American Heart Association, gaining 2–3 lbs over 24 hours, or 5 lbs in a week, could be an early sign of heart failure. People who have a history of kidney disease should also pay close attention.

Left unchecked, rapid weight gain can lead to obesity, which increases the risk of several serious health conditions. According to the CDC, obesity contributes to the development of high blood pressure, high cholesterol, other heart disease, Type 2 diabetes, asthma, sleep apnea, joint problems like osteoarthritis, and gallbladder issues.

How is the cause of rapid weight gain diagnosed?

Since there are so many potential causes for rapid weight gain, it’s often tough to nail down the cause at home, so scheduling a doctor’s appointment is the first step. The doctor may measure your body mass index (BMI), take a comprehensive history, and “a patient could undergo a combination of blood work and hormone evaluations alongside other lifestyle-identifying assessments, which may determine their diagnosis,” Dr. Chichak says. These assessments may include questions about the patient’s medical history and lifestyle habits like diet, exercise, sleep, tobacco use, alcohol consumption, and more.

From there, they may have an idea of what’s causing the sudden weight gain, and they can order blood tests that may reveal conditions like hypothyroidism, polycystic ovary syndrome, diabetes, metabolic syndrome, or Cushing’s Syndrome. If they suspect certain conditions, the doctor may order other tests, like an ultrasound, to confirm PCOS or hypothyroidism. They may also order a psychological evaluation or ask mental health-related questions. If they suspect a medication may be causing weight gain, they might prescribe an alternative to see if the weight decreases.

After the healthcare provider has diagnosed the cause, “there needs to be regular follow-ups to ensure there are no changes and to readjust any medications that might not be effective,” Dr. Chichak says. These follow-ups also help the doctor address any chronic conditions that might be contributing.

How to stop rapid weight gain

“Depending on the cause of rapid weight gain, it can be stopped or reversed, but the cause must first be identified,” Best says. “Weight gain related to lifestyle factors such as physical activity or diet, making changes to these areas can help reduce weight, while weight gain caused by stress, hormone changes, and poor sleep may be improved by making positive changes in these areas as well.” However, she says medications may be necessary to target causes of weight gain, such as hypothyroidism or insulin resistance.

Sometimes, a combination approach is the best way to treat rapid weight gain. For example, someone who has PCOS might respond well to lifestyle changes and a medication like metformin. In contrast, someone with hypothyroidism might need thyroid replacement medication and follow-up labs to confirm the thyroid replacement dose is correct for that individual patient. Someone with chronic stress might benefit from therapy, meditation, and anti-anxiety medications. Sometimes, medications like GLP-1 receptor agonists or appetite suppressants might help as well.

When the weight gain is medication-related, it might be necessary to discontinue or lower the dosage. In these cases, the doctor will typically prescribe an alternative drug or a different type of treatment.

Regardless of the cause, rapid weight gain treatments typically also involve a healthy diet, regular exercise, and adequate sleep. According to Dr. Chichak, “an active weight control program is a customized multi-step plan designed around sustainable changes in lifestyle which encompasses nutrition, exercise, and even psychotherapy to clinically manage eating behaviors centered on emotional and psychological triggers.”

Regardless, when determining how to get rid of rapid weight gain, it’s crucial to consult a doctor, who can help diagnose the specific cause and design an appropriate plan of action.

Most importantly, see a doctor to determine the underlying cause.

Rapid weight gain has many causes, including lifestyle habits, certain medications, medical conditions like hypothyroidism and PCOS, stress, sleep issues, and hormonal fluctuations. If these issues aren’t addressed, it’s often difficult to stop or reverse the increase in body weight. Medications vary based on the condition but can include weight loss drugs, diet, exercise, or other medical procedures. But the first step is getting an accurate diagnosis, so seeing a doctor is important. They can develop a treatment plan by assessing your medical history, medications, health metrics, and lifestyle, and help you start shedding those extra pounds. 

What’s next? Additional resources for people with rapid weight gain

Here are a few additional sources about rapid weight gain for more info and in-depth analysis.

Test and diagnostics

Treatments

Scientific studies and clinical trials