Why Does Lithium Cause Weight Gain?

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Weight gain is one of the most common side effects of many medications prescribed for bipolar disorder, including lithium.

There's no question that lithium leads to weight gain — studies show that people who take lithium to treat their condition are prone to adding weight, especially if they're being treated long-term.

But it's not entirely clear why this problem with weight gain occurs. Researchers believe that lithium may impact your hunger levels or the hormones your body uses to store fat and control blood sugar, leading to weight gain and other unhealthy effects, such as high cholesterol.

However, in this case, cause and effect hasn't been proven.

Lithium and Weight Gain

Weight gain was noted as a side effect almost immediately when psychiatrists started using lithium to treat bipolar disorder. In early drug trials using lithium, about 20% of patients complained specifically of weight gain.

Not everyone gains weight while on lithium, but it's a pretty common side effect. A variety of different medical studies have reported that people typically gain between nine and 14 pounds when placed on lithium. The majority of this weight gain seems to occur within the first two years of treatment, and it's a major reason why some people discontinue their drug therapy.

People who are overweight before starting lithium treatment may be more likely to gain weight from the medication.

However, lithium is far from alone when it comes to weight gain from bipolar disorder medications. Depakote (generic name: valproate), Clozaril (generic name: clozapine) and Zyprexa (olanzapine) also can cause significant weight gain, as can other bipolar disorder medications.

Why Do People Gain Weight from Lithium?

That's just not clear, although there are several theories.

There are several hormones involved in hunger and weight gain. One of these — serotonin — impacts appetite. Lithium changes how your body produces and uses serotonin, which may lead to an increased appetite (and the resulting weight gain).

However, one study that looked at hunger in people without bipolar who took lithium found no major impact on hunger.

Lithium also causes increased thirst, and another unproven theory is that this thirst leads people to consume high-calorie fluids such as sugary sodas and juices.

It's also possible that lithium changes the levels of your fat storage-regulating hormones directly, leading your body to store more calories as fat. The drug may also cause your metabolism to slow down, which means you'll burn fewer calories in general (and again, store more as fat).

Coping with Lithium-Induced Weight Gain

Weight gain is certainly an unwanted side effect of lithium treatment. However, there are several common sense steps you can take to minimize and perhaps even avoid this particular side effect:

  • Watch your consumption of high-calorie beverages, including sodas, juices and sugary coffee drinks. When you get thirsty, drink water or something that doesn't contain calories.
  • Start a regular exercise program. If you already have one, make sure to continue it.
  • Monitor your weight. If it starts to creep up, talk to your doctor about additional steps you can take to avoid further weight gain (and hopefully lose the weight you've already gained).

More information on lithium as a treatment for bipolar disorder:

Part 1: Lithium: History of the First Mood Stabilizer
Part 2: Lithium: Necessary Tests and Potential Side Effects
Part 3: Lithium: Major Precautions and Warnings


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Garland EJ et al. Weight gain with antidepressants and lithium. Journal of Clinical Psychopharmacology. 1988 Oct;8(5):323-30.

Printz D et al. Weight Gain in Bipolar Disorder: Causes and Treatments. Primary Psychiatry. 2003;10(11):29-36.

Shrivastava A et al. Weight-Gain in Psychiatric Treatment: Risks, Implications, and Strategies for Prevention and Management. Mens Sana Monographs. 2010 Jan;8(1):53-68.

Vendsborg PB et al. Lithium treatment and weight gain. Acta Psychiatrica Scandinavica. 1976 Feb;53(2):139-47.

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