The Link Between Lithium and Weight Gain

Young woman drinking water in the bedroom
Miguel Sanz / Getty Images

The mood-stabilizing drug lithium remains an effective mainstay of treatment for bipolar disorder—but unfortunately, it can cause weight gain for some people. Although the possibility of gaining weight while taking lithium is well known, this side effect does not affect everyone who takes the medication.

At a Glance

Lithium can cause weight gain. However, research suggests that lithium causes less weight gain than other medications that are also used to treat bipolar disorder. The exact causes of weight gain aren't clear, but changes in activity, food intake, and thyroid function may play a role. If you are concerned about gaining weight while taking lithium, there are steps you can take to ensure your bipolar disorder is well-managed while still maintaining a healthy body weight.

Does Lithium Cause Weight Gain?

One older study found that approximately 25% of people gain weight from taking lithium. After analyzing all relevant published medical studies, the authors reported an average weight gain of 10 to 26 pounds among those who experience this troubling side effect.

While lithium can cause weight gain for some individuals, more recent research suggests that lithium leads to less weight than other medications used to treat bipolar disorder.

A 2022 systematic review and meta-analysis concluded that lithium did not lead to significant weight gain compared to placebo. A 2023 case-control study found that lithium led to more weight gain than lamotrigine, but less than alternative medications including olanzapine, quetiapine, and valproate.

Although the biological mechanisms leading to lithium-related weight gain are unclear, researchers speculate that several processes are likely involved. Additionally, several factors can influence the likelihood of gaining weight while you're taking lithium.

Timing and Risk Factors for Lithium Weight Gain

Most people with bipolar disorder take lithium long term to stabilize mood and prevent manic and depressive episode relapses. Your risk of gaining weight while taking lithium is greatest during the first two years of treatment. This risk might be increased if you're already carrying some excess weight when you start taking the medication.

Lithium-related weight gain appears to level off after the first two years, although you might also gain weight for other reasons unrelated to the medication.

Additionally, evidence suggests that the risk of lithium-related weight gain could be dose-dependent. This means that the likelihood of weight gain increases along with the amount of lithium in your bloodstream. However, not all research studies have found this relationship, as noted in a study published in 2016 by the International Journal of Bipolar Disorders study.

Taking other medications that might also cause weight gain along with lithium also increases your risk of putting on extra pounds. Common examples of such drugs include:

Why Does Lithium Cause Weight Gain?

Despite the fact that lithium has been used in the United States for the treatment of treat bipolar disorder since 1970, the mechanisms that provoke weight gain in some people remain unclear. Several theories have been proposed. These processes may work alone or in combination to cause weight gain in people on lithium therapy.

Regaining Previously Lost Weight

Early weight gain after starting lithium therapy could represent regaining pounds that were previously lost unintentionally. This situation might apply if you experienced a manic episode—which can lead to weight loss due to disinterest in eating and increased activity—before starting lithium.

Increased Thirst

Lithium often triggers increased thirst. Quenching your thirst with high-calorie beverages, such as full-calorie soda or fruit juice, can contribute to weight gain. Lithium might also cause sodium and water retention in people who consume a high-salt diet, leading to increased body weight.

Reduced Thyroid Function

Reduced thyroid function, or hypothyroidism, is a well-known potential complication of long-term lithium treatment. This condition leads to a reduced metabolic rate, leading to weight gain.

Women taking lithium are significantly more likely to develop hypothyroidism than men.

One study found that 32% of people with bipolar disorder who were on lithium therapy developed a thyroid disorder. Of these individuals, 79% developed hypothyroidism that was then corrected with thyroid medication.

This suggests that if you do experience reduced thyroid function after taking lithium, your doctor can prescribe medications that can correct your hypothyroidism and minimize the risk of weight gain.

Other Hormones

Other hormones and brain signaling chemicals that affect hunger, blood sugar regulation, and fat and energy storage might play a role in lithium-related weight gain. As these processes are very complex and regulated at multiple levels in the body, additional research is needed to determine the possible influence of lithium.

When to See a Doctor

Contact your doctor right away if you develop any signs or symptoms that might suggest an underactive thyroid gland such as:

  • A lump near your Adam's apple
  • Dry hair and/or skin
  • Feeling cold most of the time
  • Forgetfulness
  • Irregular menstrual periods
  • Unexplained constipation
  • Unusual sensations in your hands or feet

Preventing Lithium Weight Gain

We understand your concern about gaining weight while on lithium therapy. Weight gain is understandably distressing both in terms of your self-image, and your physical and mental well-being.

Keep in mind, however, that lithium-associated weight gain only occurs in approximately 25% of people who take the medication.

Additionally, there are several steps you can take to minimize and perhaps even avoid this side effect, including:

Stick to a Healthy Diet

Limit your consumption of high-calorie, sugary beverages, such as sodas, fruit juices, sugary coffee drinks, and smoothies. Instead, drink low-calorie or noncaloric beverages to quench your thirst. Water with a twist of lemon or lime, hot or iced herbal tea, and decaffeinated coffee are a few healthful options. 

Stay Physically Active

If you're not getting much exercise currently, talk with your doctor about getting started. Remember, anything that gets you up and moving counts as physical activity. Walking is always a good option, but the possibilities are almost limitless.

Monitor Your Weight Regularly

If the number on the scale starts creeping up or your clothes feel tighter, talk with your doctor about the next steps. She might recommend consulting with a dietitian to review your current diet, changing your medications or their dosages, or another strategy. 

What This Means For You

If you do notice weight gain while taking lithium, do not stop taking your medication or change your dose without talking to your doctor first. Your doctor will want to determine what might be contributing to your weight gain, which may involve checking your thyroid function.

Your doctor can help you come up with a plan to manage your bipolar disorder and weight, either by adjusting your dose, changing your medication, or making lifestyle changes to help combat weight gain.

7 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Torrent C, Amann B, Sánchez-moreno J, et al. Weight gain in bipolar disorder: pharmacological treatment as a contributing factor. Acta Psychiatr Scand. 2008;118(1):4-18. doi:10.1111/j.1600-0447.2008.01204.x.

  2. Gomes-da-Costa S, Marx W, Corponi F, et al. Lithium therapy and weight change in people with bipolar disorder: A systematic review and meta-analysisNeurosci Biobehav Rev. 2022;134:104266. doi:10.1016/j.neubiorev.2021.07.011

  3. Greil W, de Bardeci M, Müller-Oerlinghausen B, et al. Controversies regarding lithium-associated weight gain: case–control study of real-world drug safety data. Int J Bipolar Disord. 2023;11(1):34. doi:10.1186/s40345-023-00313-8

  4. Gitlin M. Lithium side effects and toxicity: Prevalence and management strategies. Int J Bipolar Disord. 2016;4:27. doi:10.1186/s40345-016-0068-y

  5. Kibirige D, Luzinda K, Ssekitoleko R. Spectrum of Lithium-Induced Thyroid Abnormalities: A Current PerspectiveThyroid Res. 2013 Feb 7;6(1):3. doi:10.1186/1756-6614-6-3

  6. Joseph B, Nunez NA, Pazdernik V, et al. Long-term lithium therapy and thyroid disorders in bipolar disorder: A historical cohort studyBrain Sci. 2023;13(1):133. doi:10.3390/brainsci13010133

  7. Bauer I, Gálvez J, Hamilton J et al. Lifestyle interventions targeting dietary habits and exercise in bipolar disorder: A systematic reviewJ Psychiatr Res. 2016;74:1-7. doi:10.1016/j.jpsychires.2015.12.006

Additional Reading

By Marcia Purse
Marcia Purse is a mental health writer and bipolar disorder advocate who brings strong research skills and personal experiences to her writing.