The Hidden Cost of Seizure Medications: Why Your Bones May Be Breaking Down

If you've been taking antiseizure medications for years, your bones may be paying a silent price. Certain antiseizure drugs accelerate how your liver breaks down vitamin D, which directly undermines your body's ability to absorb calcium and maintain bone density. This medication-induced bone loss is real, often goes undetected, and can lead to fractures that take longer to heal than expected.

How Do Antiseizure Medications Damage Bone Health?

The mechanism is surprisingly straightforward, though the consequences are serious. Antiseizure medications speed up your liver's metabolism of vitamin D, breaking it down faster than your body can use it. Here's why this matters: vitamin D must undergo two transformations to become active. First, your liver converts it to 25-hydroxyvitamin D (25(OH)D), and then your kidneys activate it further. When antiseizure drugs accelerate this liver metabolism, the vitamin D gets broken down too quickly, leaving less active vitamin D available to do its job.

Without adequate active vitamin D, your intestines cannot absorb calcium properly. This triggers a cascade: your body senses low calcium levels and pulls calcium directly from your bones to maintain blood calcium balance. Over time, this bone resorption—essentially calcium withdrawal from your skeleton—leads to weakened bones and increased fracture risk.

Why Standard Tests Might Not Catch the Problem

Here's where things get tricky. Many people on long-term antiseizure therapy have normal-looking calcium and vitamin D test results, yet their bones are still deteriorating. The issue is that standard serum calcium and vitamin D tests measure overall levels but don't capture the absorption problem or the accelerated metabolism happening at the cellular level. This gap between "normal" test results and actual bone damage can delay diagnosis by years.

One patient on antiseizure medications for 45 years described the frustration: "I have reg D and Calcium tests. Both say normal so I am suspect of the tests' ability to detect metabolism and absorption". This patient's femoral neck (hip bone) density score was -2.6, indicating significant bone loss, despite reassuring lab work.

What Tests Should You Actually Be Getting?

If you're on long-term antiseizure therapy, ask your doctor about more comprehensive monitoring. The key tests to request include: Serum 25-hydroxyvitamin D (25(OH)D) test: This is the standard test for measuring vitamin D status, but it should be interpreted carefully in the context of your medication use. Serum calcium and parathyroid hormone (PTH) levels: These help monitor your body's calcium balance and whether your parathyroid gland is compensating for low calcium by pulling it from bones. Bone-specific alkaline phosphatase (bALP): This marker shows whether your bones are actively building new bone tissue or losing it. DEXA scan: This imaging test measures bone mineral density and should be done regularly if you're on medications known to affect bone metabolism. The combination of these tests gives a much clearer picture than calcium and vitamin D levels alone.

Higher Vitamin D Doses Are Often Necessary

The standard solution is to prescribe higher doses of vitamin D to compensate for the accelerated breakdown. Because antiseizure medications speed up liver metabolism, patients on these drugs typically need more vitamin D from food, supplements, or sun exposure than the general population. However, the exact dose varies based on which antiseizure medication you're taking, your baseline vitamin D levels, and how your body responds.

One patient who discovered osteoporosis after a compression fracture of the spine while on low-dose prednisone (a different bone-damaging medication) found success with aggressive treatment. "I see a bone health professional who prescribed more calcium and vitamin D supplements, as well as Tymlos, a daily injection you take for two years," they explained. "I just finished my first year and blood markers indicated I'm building bone. Evidently there is a way to reverse osteoporosis".

The Real-World Impact: Fractures That Won't Heal

The consequences of undetected medication-induced bone loss can be serious. One patient on antiseizure medications fractured their leg and foot in a fall and experienced delayed healing. "Took more time to heal (4.5 months) than normal (2 months). Orthopedists were confounded," they reported. The delayed healing is a red flag that bone quality has been compromised.

If you've been on antiseizure medications for more than a few years, especially at higher doses, it's worth having a conversation with your doctor about bone health screening. Don't assume that normal calcium and vitamin D test results mean your bones are safe. Ask specifically about medication-induced bone loss, request the comprehensive testing panel, and consider seeing a bone health specialist who understands the unique challenges of medication-related osteoporosis. Catching the problem early—before fractures occur—makes a significant difference in preventing long-term complications.