Do opioids make you lose or gain weight? Understanding the complex effects

October 7, 2025 •

5 min read

Studies have shown that medications like methadone can lead to significant weight gain, with one study of Veterans finding an average increase of about 10 pounds over one year. This highlights the nuanced answer to whether opioids make you lose or gain weight, as the effect is not uniform and depends on several factors.

Quick Summary

Weight changes from opioid use vary, with some people gaining weight from increased appetite and inactivity, while others lose it due to nausea or appetite suppression. Specific medications for opioid use disorder also show different effects.

Key Points

Weight Effects Vary by Drug and User: The effect of opioids on weight is not uniform, with some individuals experiencing weight gain and others weight loss, influenced by drug type, dose, and individual health factors.
Weight Gain Linked to Chronic Agonist Use: Long-term use of opioid agonists like methadone and, to a lesser extent, buprenorphine, is frequently associated with weight gain due to increased appetite and reduced activity.
Weight Loss Often Associated with Acute or Illicit Use: In some cases, such as initial opioid use or illicit heroin addiction, weight loss can occur due to appetite suppression, nausea, and financial constraints impacting nutrition.
Mechanisms Include Appetite Changes and Inactivity: Opioids can stimulate cravings for sugary foods and cause sedation, leading to higher caloric intake and lower energy expenditure, both contributing to weight gain.
Hormonal and Metabolic Factors Play a Role: Chronic opioid use can cause hormonal imbalances (e.g., lower testosterone, higher cortisol) and metabolic issues, which affect body composition and fat storage.
Medication for Opioid Use Disorder (MOUD) Has Varying Effects: Methadone typically causes more weight gain than buprenorphine, while the antagonist naltrexone is generally weight-neutral or can aid in weight loss.
Weight Management is a Proactive Strategy: Addressing weight fluctuations requires a balanced diet, regular exercise, managing side effects like constipation, and regular consultation with a healthcare provider.

The impact of opioid use on body weight is not a simple matter of gain or loss, but a complex interplay of the drug's pharmacological effects, duration of use, and individual health factors. While some people experience significant weight gain, others may notice a decrease in their body weight. The final outcome is influenced by how the drug affects a person's metabolism, appetite, and lifestyle.

The Dual Nature of Opioids and Body Weight

Opioids affect the central nervous system in ways that can lead to both increased and decreased caloric intake and energy expenditure. The effects can be seen in both patients using prescription opioids for pain management and those with opioid use disorder. The reasons behind these weight fluctuations are multifaceted, involving changes to the body's reward systems, hormone levels, and digestive processes.

The Drivers Behind Opioid-Induced Weight Gain

For many, long-term opioid use is associated with weight gain. Several mechanisms contribute to this effect:

Sedation and Decreased Physical Activity: Opioids are known for their sedative effects, which can cause drowsiness and lethargy. This often leads to a reduction in physical activity, meaning fewer calories are burned and more are stored as fat. A person with chronic pain, whose mobility is already limited, may become even less active while on opioids.
Increased Appetite and Cravings: Opioid agonists, particularly methadone and buprenorphine, have been linked to increased appetite and a specific craving for sweet and high-sugar foods. This dysregulated reward system encourages comfort eating to provide feelings of pleasure, especially in the absence of the drug or during treatment.
Slowed Metabolism and Digestion: Opioids can slow down the digestive system, a common side effect known as constipation. While this can cause temporary weight gain and bloating from fluid retention and a backlog of waste, chronic use can also reduce metabolism over time, further contributing to fat storage.
Fluid Retention: Certain opioids can lead to fluid retention, causing a temporary increase on the scale that is not due to body fat.
Hormonal Imbalances: Long-term use can disrupt the endocrine system, decreasing testosterone levels and potentially increasing cortisol. Lower testosterone can lead to reduced muscle mass and increased fat, while higher cortisol is associated with increased appetite and abdominal fat storage.

Opioids and the Potential for Weight Loss

In some cases, especially at the beginning of use or with illicit drugs, opioids can lead to weight loss. The factors involved include:

Appetite Suppression: Initial or short-term opioid use can suppress appetite, especially if accompanied by gastrointestinal issues like nausea. This reduces caloric intake and can lead to weight loss.
Nausea and Vomiting: Nausea and vomiting are common side effects, particularly when first starting opioids or taking high doses. These symptoms make eating unpleasant and can lead to malnutrition and weight loss.
Lifestyle and Malnutrition: In cases of severe opioid use disorder, particularly with illicit drugs like heroin, a person's life is often consumed by drug use. Financial resources are prioritized for the drug rather than for food, leading to malnutrition and weight loss. Many individuals starting opioid use disorder treatment are underweight as a result.

Medication for Opioid Use Disorder (MOUD) and Weight

Medication-assisted treatment (MAT) for opioid use disorder has different implications for weight management depending on the type of medication. The following table compares the typical effects of methadone, buprenorphine, and naltrexone.


Feature	Methadone (Opioid Agonist)	Buprenorphine (Partial Agonist)	Naltrexone (Opioid Antagonist)
Effect on Weight	Significant weight gain is a common side effect, especially long-term.	Modest weight gain observed in some studies, particularly long-term, though effects can vary.	Weight-neutral or can promote weight loss, sometimes used in combination with other drugs for obesity.
Weight Gain Mechanism	Increases appetite (especially for sugary foods), reduces metabolism, and contributes to a more sedentary lifestyle.	Appetite effects are less pronounced than methadone, but can still lead to weight gain over time due to hormonal changes and lifestyle improvements.	Can reduce cravings for palatable, high-sugar foods by blocking opioid receptors.
Hormonal Impact	Known to affect hormone levels, contributing to metabolic changes.	May also affect hormonal balance with chronic use.	No significant link to hormonal changes that promote weight gain in the same way as agonists.
Considerations	Monitoring diet and exercise is crucial due to the high risk of weight-related health issues.	Weight changes are typically less drastic than with methadone but still require attention.	May be a preferred option for individuals with risk factors for obesity or diabetes.

Managing Weight While on Opioids

Regardless of whether a person experiences weight gain or loss, it's important to address body weight proactively. Here are some strategies that can help:

Emphasize a Balanced Diet: Focus on whole foods, lean proteins, fruits, vegetables, and complex carbohydrates to provide necessary nutrients. Limiting highly processed foods and sugary drinks can counteract increased cravings for sweets.
Incorporate Regular Physical Activity: Even gentle exercise, like walking, can help regulate metabolism, manage weight, and improve mood and energy levels. Discuss appropriate exercise with a healthcare provider, especially if dealing with chronic pain.
Stay Hydrated: Drinking plenty of water can help with fluid balance, improve digestion, and manage appetite cues.
Address GI Side Effects: Managing constipation with fiber, fluids, and, if necessary, medication can alleviate bloating and digestive discomfort.
Meal Planning: Establishing a consistent eating schedule and planning meals can help regulate metabolism and prevent unhealthy snacking.
Consult a Healthcare Provider: Your doctor can help monitor your weight, recommend dietary changes, and, if appropriate, adjust your medication plan. In some cases, working with a dietitian or nutritionist can also be beneficial.

Conclusion

Do opioids make you lose or gain weight? The answer is not a simple one, as the effects are highly variable and depend on individual factors, the type of opioid, and the duration of use. While chronic use of opioid agonists like methadone is commonly linked to weight gain through appetite changes, metabolic shifts, and decreased activity, certain situations, like initial use or heroin addiction, can lead to weight loss. For those in recovery or managing chronic pain, proactive weight management through diet, exercise, and professional guidance is crucial for overall health.

Visit the National Institute on Drug Abuse (NIDA) for more information on the effects of medications like buprenorphine and methadone.

Frequently Asked Questions

No, not all opioids cause weight gain, and the effect can vary significantly depending on the specific drug and individual. While many opioid agonists, especially with long-term use, are linked to weight gain, others may cause weight loss, especially initially due to side effects like nausea.

Weight gain is often linked to chronic use and factors like increased cravings for sweets, reduced metabolism, and inactivity due to sedation. Weight loss can be caused by initial appetite suppression, nausea, or the malnutrition associated with long-term illicit drug use.

Yes, methadone treatment is commonly associated with weight gain. Studies have shown significant increases in body weight over time for patients on methadone maintenance due to increased appetite and metabolic changes.

Buprenorphine's effect on weight is less pronounced than methadone's. Some studies show modest weight gain, particularly long-term, while others report little to no change in the first few months. Weight gain is still a possibility and should be monitored.

Managing your weight involves a combination of strategies, including incorporating regular physical activity, focusing on a healthy and balanced diet, staying hydrated, managing constipation, and working closely with your doctor to create a personalized plan.

Yes, opioids can affect appetite and taste preferences. Chronic use of opioid agonists can lead to increased cravings for sweet and palatable foods, stimulating a part of the brain's reward system.

Weight gain, especially to the point of being overweight or obese, can increase the risk of serious health issues like heart disease and diabetes. This risk, compounded with other health complications related to opioid use, emphasizes the importance of managing weight during treatment.