Lithium is primarily prescribed to treat bipolar disorder. It remains one of the oldest and most effective psychiatric medications in use, approved to manage acute manic episodes and to prevent future episodes from recurring. International treatment guidelines consistently rank it as a first-line option for bipolar disorder across nearly every phase of the illness.
Bipolar Disorder: The Primary Use
Lithium’s core role is treating the manic episodes that define bipolar disorder, sometimes called manic-depressive illness. During a manic episode, a person may feel abnormally energized, sleep very little, take unusual risks, or experience racing thoughts that spiral out of control. Lithium helps bring these episodes under control and, when taken daily, reduces how often and how severely they return.
The 2023 update to the CANMAT/ISBD international guidelines, one of the most widely referenced clinical standards, lists lithium as a first-line treatment for acute mania, acute bipolar depression, and long-term maintenance therapy in both bipolar I and bipolar II disorder. It holds this ranking for adults, older adults, and children and adolescents. Few psychiatric medications have maintained that breadth of endorsement for as long as lithium has.
How Well It Prevents Relapse
Lithium’s strongest evidence is in preventing manic relapses. A major meta-analysis of randomized controlled trials published in the American Journal of Psychiatry found that lithium reduces the risk of manic relapse by roughly 40%, cutting the rate from about 24% on placebo to 14% on lithium. For overall relapses of any kind, 60% of people on placebo relapsed compared with 40% on lithium.
Its protection against depressive episodes is real but more modest. The same analysis found the depressive relapse rate dropped from 32% on placebo to 25% on lithium, a smaller and statistically less consistent difference. This is why lithium is sometimes paired with other medications to better cover the depressive side of bipolar disorder.
Off-Label and Additional Uses
Beyond its approved indication for bipolar disorder, clinicians sometimes prescribe lithium as an add-on for treatment-resistant depression, meaning depression that hasn’t responded adequately to standard antidepressants. This use has decades of clinical support, though it isn’t part of lithium’s formal labeling.
Lithium has also been studied extensively for its potential to reduce suicidal behavior, particularly in people with mood disorders. Some observational studies have suggested a protective effect, though a large randomized trial in veterans with major depression or bipolar disorder found no significant difference in repeated suicide-related events between lithium and placebo. The question remains actively debated.
How Lithium Works in the Brain
Lithium’s exact mechanism isn’t fully mapped, but researchers have identified several key pathways. One of the most studied involves an enzyme called GSK-3, which plays a role in cell signaling, brain cell survival, and how neurons communicate. Lithium directly inhibits this enzyme and also activates a separate pathway (through a protein called Akt) that further dials down GSK-3 activity. The combined effect appears to stabilize mood-related signaling networks that become dysregulated in bipolar disorder.
Lithium also affects how cells process a signaling molecule called inositol, which is involved in transmitting messages between brain cells. By dampening overactive signaling in these pathways, lithium appears to reduce the runaway neural activity associated with mania while also promoting the long-term health and resilience of brain cells.
Blood Monitoring and Therapeutic Levels
Lithium has a narrow therapeutic window, meaning the effective dose and the toxic dose aren’t far apart. This makes regular blood monitoring essential. The target blood level for most people is between 0.5 and 1.2 mmol/L, measured from a blood draw taken 8 to 12 hours after the last dose. Levels above 1.6 mmol/L are considered critical and can cause serious toxicity.
When you first start lithium, your blood will be checked frequently to dial in the right dose. Once levels are stable, testing typically moves to every few months. Kidney function and thyroid function also need monitoring, generally every six months. People over 65 or those with other health conditions may need checks every three months.
Common Side Effects
The most frequently reported side effects of lithium include a fine hand tremor, increased thirst, and more frequent urination. Some people notice weight gain or mild digestive upset, particularly when first starting the medication. These effects are often dose-related, meaning they tend to improve if the dose is adjusted or if an extended-release formulation is used instead of the standard version.
Over the long term, lithium can affect the thyroid gland, sometimes leading to an underactive thyroid that requires treatment with thyroid hormone. It can also gradually affect kidney function in some people, which is why those regular blood tests matter. The risk of kidney problems is higher in people who also have high blood pressure, diabetes, or heart failure.
Drug Interactions to Be Aware Of
Because lithium is eliminated almost entirely through the kidneys and isn’t broken down by the liver like most drugs, anything that changes kidney function or sodium balance can push lithium levels up or down. Several common medication categories can raise lithium to potentially dangerous levels:
- NSAIDs like ibuprofen and naproxen reduce how quickly the kidneys clear lithium
- ACE inhibitors and ARBs, commonly prescribed for blood pressure, have the same effect
- Diuretics, particularly thiazide-type water pills, reduce sodium excretion and cause lithium to build up
- SSRIs, a common class of antidepressants, can interact with lithium and in rare cases contribute to a condition caused by excess serotonin activity
Dehydration itself is also a risk factor. Anything that causes significant fluid loss, from intense exercise to stomach illness to simply not drinking enough water in hot weather, can concentrate lithium in your blood and tip levels into the toxic range. Staying well-hydrated and maintaining consistent salt intake are practical habits that help keep levels stable.
Who Can Take Lithium
Lithium is approved for adults and children aged 7 and older (weighing more than 30 kg) in standard formulations, and for those 12 and older in extended-release tablets. It is not recommended for children under 7. For older adults, it remains a first-line option, though dosing tends to be more conservative and monitoring more frequent because kidney function naturally declines with age.
Despite being one of the simplest substances prescribed in psychiatry (it’s a naturally occurring element, not a complex synthetic molecule), lithium requires more active management than many medications. The blood tests, the attention to hydration, and the awareness of drug interactions make it a medication that works best when both the prescriber and the person taking it stay engaged in the process. For those who tolerate it well, lithium remains one of the most effective tools available for keeping bipolar disorder stable over the long term.