Genes, Drug Allergy and Side Effects: Why Do Some React Severely?

Key Takeaways

• Some severe drug allergies have a genetic basis that can be predicted in advance.
• The HLA gene group is linked to severe reactions to certain drugs, such as SJS/TEN drug rashes.
• Thai/Asian people have a higher frequency of some risk genes than other populations.
• Gene testing before using certain drugs can prevent serious harm.

Why can the same drug be fine for one person but cause a severe, life-threatening rash in another? Part of the answer lies in genes. This article explains how genetics relates to drug allergy and why gene testing before certain medications matters.

Drug Reactions Aren't the Same for Everyone

Each person responds to drugs differently, from effectiveness to side effects. Some develop severe drug reactions affecting skin and internal organs, which can be life-threatening. These reactions aren't random — they often have genetic factors behind them.

HLA Genes and Severe Drug Allergy

The HLA gene group, which controls the immune system, plays a key role. A well-known example is the link between certain HLA types and reactions to some anticonvulsants, gout drugs, and antivirals, which can cause severe drug rashes called SJS/TEN (Stevens-Johnson Syndrome / Toxic Epidermal Necrolysis) — a medical emergency. In particular, for the drug carbamazepine, research in Thai patients found that up to 88% of SJS/TEN cases carried the HLA-B*15:02 allele (odds ratio around 55) (Tassaneeyakul et al., Epilepsia, 2010). This connects directly with HLA typing.

Why Should Thai/Asian People Pay Special Attention?

The frequency of some risk genes differs by ethnicity. Asian populations, including Thai people, have a higher frequency of certain HLA alleles linked to severe drug reactions than Westerners — HLA-B*15:02 is found in around 15% of the general Thai population, far higher than in Westerners (Sukasem et al., Journal of Immunology Research, 2018). That makes gene testing before starting certain drugs especially worthwhile here, aligning with pharmacogenomics, which tailors drug use to genes.

How Does Gene Testing Help Prevent Harm?

For certain drugs with clear gene associations, a doctor may recommend testing before starting. If a risk gene is found, a safer alternative drug can be chosen. This is "prevent-before-it-happens" medicine using real genetic data. A single test provides information you can use for life.

Author's Final Note

Severe drug allergy is partly preventable with genetic information. Knowing your gene status before using high-risk drug groups is a worthwhile safety investment. That said, testing and interpretation should always be under the care of a doctor or pharmacist. Start understanding your genes with a DNA test.

References

1. Tassaneeyakul W, Tiamkao S, Jantararoungtong T, et al. Association between HLA-B*1502 and carbamazepine-induced severe cutaneous adverse drug reactions in a Thai population. Epilepsia. 2010;51(5):926-930. PubMed
2. Sukasem C, et al. Association between HLA-B Alleles and Carbamazepine-Induced Maculopapular Exanthema and Severe Cutaneous Reactions in Thai Patients. Journal of Immunology Research. 2018;2018:2780272. NCBI PMC