Yes — the active ingredient is metabolized by a gene known to vary between individuals.
Relevant genes: HLA-B
Used for: Seizures, bipolar disorder, trigeminal neuralgiaTegretol (carbamazepine) carries one of the most consequential pharmacogenetic warnings in modern prescribing, and unlike most pharmacogenetic stories, it has nothing to do with how the drug is metabolized. It's about your immune system's reaction to it. People who carry the HLA-B*15:02 variant have a dramatically elevated risk of developing Stevens-Johnson syndrome or toxic epidermal necrolysis on carbamazepine. These are severe skin reactions where large areas of skin blister and slough off, and they can be fatal. HLA-B*15:02 is uncommon in people of European or African descent but carried by roughly 10 to 15 percent of people of Han Chinese, Thai, Malay, Indian, and Filipino ancestry. The FDA now recommends HLA-B*15:02 screening before starting carbamazepine in patients from these populations.
Carbamazepine is also metabolized by CYP3A4 and CYP2C9, but the clinically dominant pharmacogenetic concern is HLA-B*15:02 and skin reactions. A second HLA allele, HLA-A*31:01 (more common across populations), is also linked to carbamazepine hypersensitivity, though the reactions are generally less severe. For patients carrying either allele, alternative mood stabilizers or antiepileptics are usually preferred. Oxcarbazepine (a close relative) also carries risk in HLA-B*15:02 carriers, so it's not a safe substitute.
Read the full carbamazepine genetics guide →Published guidance from FDA on how carbamazepine should be dosed or substituted based on your HLA-B phenotype.
| Phenotype | What it means | Recommendation | Evidence |
|---|---|---|---|
|
*15:02
HLA-B
|
You carry a gene variant that puts you at high risk for severe, potentially life-threatening skin reactions if you take carbamazepine. An alternative medication is strongly recommended. |
FDA
Do not use carbamazepine in HLA-B*15:02 positive patients unless potential benefits clearly outweigh risks. Consider alternative anticonvulsants.
|
Strong |
Source: FDA
HLA-B variants don't affect how drugs are metabolized. They affect your immune system's reaction to them. Specific HLA-B alleles are strongly linked to severe skin reactions to drugs like abacavir (HIV), carbamazepine (seizures, bipolar), and allopurinol (gout).
Screening for HLA-B*57:01 before abacavir, and HLA-B*15:02 before carbamazepine in at-risk populations, is now standard of care in much of the world.
Browse the full drug-class: Anticonvulsants.
If you or a family member has ancestry from East or Southeast Asia and is about to start carbamazepine, ask whether HLA-B*15:02 testing has been done. Many hospitals now test automatically when carbamazepine is ordered for patients from at-risk populations, but not all. The test is cheap, results come back in days, and the alternative (discovering the reaction by developing it) is catastrophic. Patients who've been stable on carbamazepine for years without a reaction almost certainly don't carry the allele, and the acute risk is highest in the first few months of therapy.
The FDA and most guidelines target testing to patients of Asian ancestry (particularly East and Southeast Asian) because the allele is rare elsewhere. For patients of European or African descent, the clinical yield of testing is extremely low, and most guidelines don't require it. That said, some health systems test everyone to avoid making assumptions about ancestry, and the test isn't expensive.
Almost always, the answer is no, and an alternative is chosen. The risk of Stevens-Johnson syndrome in positive patients is high enough that the risk-benefit calculus rarely favors carbamazepine. Lamotrigine, valproate, levetiracetam, and lithium (for bipolar) are common alternatives depending on the indication. Oxcarbazepine is structurally similar to carbamazepine and is not a safe substitute for HLA-B*15:02 positive patients.
HLA-A*31:01 is a separate allele associated with a different, usually less severe spectrum of carbamazepine hypersensitivity. It's more common across populations (around 2 to 5 percent in most groups). Some guidelines recommend testing for both HLA-B*15:02 and HLA-A*31:01; others prioritize only HLA-B*15:02 because the skin reactions are more severe. CPIC covers both in its carbamazepine guideline.
This page describes the general pharmacogenetics. A Gene2Rx report analyzes your own DNA to tell you which metabolizer group you fall into, across every medication.
Get your report Look up another medicationInformational only — not medical advice. Pharmacogenetic guidance describes population-level patterns; your individual response depends on many factors. Never start, stop, or change a medication without talking to your prescribing clinician.