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Lithium Weight Gain: What Is It and Why It Happens

cartoon woman on scale and is unhappy

Lithium carbonate is a prescription medication that belongs to a group of medications called mood stabilizers. These drugs are used in psychiatry to treat bipolar disorder (manic depression), bipolar affective disorder, and other mood disorders. However, like  any medication, the mood stabilizer lithium can cause side effects. 

This article will discuss one of its well-known adverse effects lithium-induced weight gain. We will also look at some tips for patients to manage body weight while on long-term lithium treatment.

How much weight gain occurs with lithium treatment?

Research indicates that 20-50% of psychiatric patients receiving lithium experience a moderate to significant body weight gain on this medicine. However, it is worth noting that not everyone who takes lithium carbonate experiences weight gain and that increased weight can vary significantly from person to person. Studies have shown that the average lithium-induced weight gain is between 4.85 and 22 lbs. 

Also, keep in mind that different causes contribute to lithium-induced weight gain - we will discuss them in more detail below.

Why do bipolar medications cause weight gain?

Bipolar patients taking lithium and other mood stabilizers can experience many adverse effects; however, these adverse effects are relatively tolerable and tend to improve as the treatment continues. One of the side effects of lithium maintenance therapy is weight gain. Scientists believe that lithium-associated weight gain occurs due to various reasons, such as increased thirst, increased appetite, alterations in metabolism, sodium retention, hormonal fluctuations, constipation, and fatigue

Causes of Lithium Induced Weight Gain

Lithium-treated patients commonly experience unwanted weight gain in the first few months of lithium maintenance therapy. Let’s look more closely at some of the reasons for body weight gain on lithium therapy in bipolar disorder patients. 

Increased appetite

Lithium carbonate can cause increased appetite as a side effect in approximately 1 out of 3 patients. Unless a person can maintain strict control of food intake to consume fewer calories, this surge in appetite caused by lithium can lead to gaining weight.

Edema or bloating

Lithium carbonate's other side effects are sodium retention when the body holds on to extra salt leading to polydipsia (increased thirst). This side effect causes a person to consume more fluids,  leading to bloating and edema (swelling), known as water weight gain. Moreover, beverages like sodas, sports drinks, and fruit juices can also contribute to weight gain in lithium-treated patients due to the high calories from these beverages.


Approximately 10% of patients treated with lithium experience constipation, which can lead to some temporary weight gain because the digested food remains in the gut.

Taste changes and cravings

Research has shown that in some bipolar patients, weight gain occurs with lithium monotherapy because lithium alters their taste. This side effect causes cravings for beverages and food that are salty, fatty,  or sugary. In addition to the increased calorie intake from these cravings, salty foods can lead to water retention, leading to weight gain.

Fatigue or lethargy

Lithium use can cause fatigue and lethargy in many patients. Decreased energy levels and tiredness can lead to less frequent exercise during lithium treatment, leading to lithium-induced weight gain. 

Hormonal changes

Bipolar patients can gain weight on lithium due to changes in the levels of hormones such as leptin, ghrelin, estrogen, testosterone, insulin, cortisol, and thyroxine (T4). These hormonal fluctuations can slow down the resting metabolic rate, increase appetite, increase fat storage, and cause changes in carbohydrate and fat metabolism – all of which can lead to weight gain. 

Cognitive effects

Lithium treatment in people with bipolar disorder can cause side effects such as confusion and memory problems. These adverse effects can indirectly cause a person to experience weight gain because the affected individual might have trouble planning healthy meals and controlling caloric intake. 

Changes in gut bacteria

Maintenance treatment with mood stabilizers like lithium carbonate can lead to changes in gut bacteria, which can lead to increased appetite, constipation, water retention, or increased fat storage, all of which can cause weight gain in lithium-treated patients. 

What factors affect weight gain during long-term lithium therapy?

As mentioned, not every bipolar patient will gain weight during lithium treatment. Multiple risk factors determine whether there will be an increase in body weight on lithium. A person’s baseline weight, lithium dose, duration of lithium treatment,  concurrent medications, lifestyle, and genetics can all play a role in the occurrence and severity of lithium-induced weight gain.

How do you stop lithium related weight gain?

Before starting the medicine, people taking lithium should record their baseline body weight and body mass index  (BMI). They should also have their weight routinely monitored during treatment. The strategies for weight loss or weight management to offset lithium weight gain mainly involve healthy eating and regular exercise. 

Despite these measures, if you are experiencing excessive weight gain while taking lithium, you might need to discuss lithium dosage modifications with your doctor (low dose lithium is less likely to cause weight gain). Your healthcare provider may order blood tests such as thyroid function tests to evaluate if hypothyroidism (underactive thyroid function) is causing weight gain. Your healthcare team may also try to manage other side effects of lithium, such as increased thirst to help with reducing water weight.

It is worth noting that although lithium can cause substantial weight change during the first 6 months of treatment, there is some evidence that the bodyweight stabilizes within a year of a lithium regimen. In other words, you might experience some significant weight gain at the beginning of the lithium treatment; however, the good news is that your body weight tends to stabilize after that initial period. It is highly recommended that you work closely with your medical team to have a reasonable weight control plan and detect other potential underlying causes that can contribute to this problem. 

If you continue to experience significant weight gain on lithium and weight management strategies are unsuccessful, you should obtain professional medical advice to discuss other treatment alternatives. Your doctor can help you transition to other mood stabilizers that are less likely to cause weight gain.


  1. https://mentalhealthdaily.com/2018/03/02/lithium-weight-gain/
  2. https://journalbipolardisorders.springeropen.com/articles/10.1186/s40345-016-0068-y