Lithium does not typically cause high blood pressure as a routine side effect, but it can raise blood pressure through several indirect pathways. High blood pressure is listed as a sign of lithium toxicity, and long-term lithium use can affect the kidneys, thyroid, and metabolism in ways that contribute to elevated readings over time.
Blood Pressure and Lithium Toxicity
The most direct link between lithium and high blood pressure occurs during lithium toxicity, when levels in the blood climb too high. Cleveland Clinic lists high blood pressure alongside rapid heart rate, confusion, and shivering as signs of toxic lithium levels. This is not the same as lithium gradually raising your blood pressure at normal doses. It’s an acute warning sign that something has gone wrong with how your body is processing the drug.
Lithium toxicity can develop in several ways. Sometimes the dose is simply too high. More often, something changes in how your kidneys clear lithium from the body. Dehydration, new medications, or a decline in kidney function can all tip levels into the danger zone. People over 50, those with existing kidney problems, and those with thyroid disease face the highest risk of chronic toxicity building up over time.
How Lithium Affects the Kidneys
The kidneys are the only way your body eliminates lithium, and lithium is not gentle on them. Long-term use is associated with several renal side effects: excessive urination, a condition called nephrogenic diabetes insipidus (where the kidneys lose the ability to concentrate urine), decreased filtration rate, and protein in the urine. These problems stem from lithium’s effect on a specific enzyme involved in tissue repair and regeneration across many organs, including the kidneys. Lithium suppresses this enzyme’s activity, which promotes inflammation-driven fluid loss in the kidneys and disrupts normal sodium handling in the renal tubules.
Why does this matter for blood pressure? Your kidneys are central to blood pressure regulation. They control how much sodium and water your body retains, and they produce hormones that influence blood vessel tone. When kidney function declines, the body’s ability to manage fluid balance weakens, and blood pressure can creep upward. This is not a sudden spike but a gradual shift that may develop over years of lithium therapy. Monitoring kidney function is standard practice during lithium treatment, with testing recommended every two to three months during the first six months and every six to twelve months after that.
The Thyroid Connection
Lithium commonly causes hypothyroidism, a condition where the thyroid gland becomes underactive. This is one of the most well-known side effects of the drug. Hypothyroidism affects the cardiovascular system in several ways. It can increase the stiffness of blood vessel walls, raise levels of LDL cholesterol, and promote fluid retention. All of these changes can push blood pressure higher, particularly diastolic pressure (the bottom number). If you’re on lithium and notice your blood pressure climbing, an underactive thyroid is one of the first things worth investigating. It’s treatable, and correcting it often helps normalize cardiovascular readings.
Weight Gain as an Indirect Factor
Many people on lithium gain weight, and this is one of the most common reasons patients want to stop taking it. Weight gain raises blood pressure through well-established mechanisms: increased insulin resistance, higher blood volume, and greater strain on the heart and blood vessels. While the blood pressure increase is not caused by lithium directly in this case, it’s a predictable downstream effect of a body change that lithium frequently triggers. Even a gain of 10 to 15 pounds can meaningfully shift blood pressure readings, especially in someone who was already near the borderline.
Dangerous Interactions With Blood Pressure Medications
If you’re taking lithium and also need treatment for high blood pressure, the choice of medication matters significantly. Several common blood pressure drugs interact with lithium in ways that can be dangerous.
ACE inhibitors are one of the most concerning. In one study, 4 out of 20 patients who started an ACE inhibitor while on lithium developed symptoms of lithium toxicity. Elderly patients face an especially high risk within the first month of combining these drugs. The mechanism is straightforward: ACE inhibitors reduce pressure inside the kidney’s filtering units, which slows the rate at which lithium is cleared from the body. Lithium levels rise, sometimes to toxic ranges, bringing the blood pressure spikes and other dangerous symptoms described above.
Diuretics (water pills) are another concern. Thiazide diuretics are particularly problematic because lithium behaves like sodium in the body. When a diuretic causes the kidneys to flush out more sodium, the kidneys compensate by reabsorbing more lithium from the same tubules. Loop diuretics also dramatically increase the risk of lithium toxicity. Even volume depletion from any cause, including sweating heavily or not drinking enough water, can trigger the same reabsorption problem.
Angiotensin receptor blockers (ARBs) carry a similar interaction risk as ACE inhibitors, though some evidence suggests certain ARBs may be better tolerated. In one case report, a patient was switched to losartan for blood pressure control without significant adverse effects on kidney function. Still, close monitoring of lithium levels is essential whenever any of these medications are combined.
NSAIDs, the common over-the-counter painkillers like ibuprofen and naproxen, also decrease kidney filtration and can push lithium levels higher. This is worth knowing because many people take these casually without realizing the interaction.
What to Watch For
If you’re on lithium, periodic blood pressure checks are a practical addition to the routine lab monitoring you’re already doing. A single elevated reading is not cause for alarm, but a pattern of rising numbers deserves attention. The key is figuring out the cause: is it a sign of lithium toxicity, a kidney issue developing over time, a thyroid change, weight gain, or a medication interaction?
Signs that suggest lithium toxicity rather than garden-variety high blood pressure include tremor, confusion, nausea, slurred speech, and a noticeably fast heartbeat alongside the elevated reading. These warrant urgent evaluation. A gradual upward trend in blood pressure without those acute symptoms points more toward the chronic mechanisms: kidney changes, thyroid dysfunction, or metabolic shifts that can be identified and managed with the right testing.