Over one-quarter (26.8%, 2429/9051) of our cohort carried a genotype associated with life-threatening drug toxicities including allopurinol- or carbamazepine-induced Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN, 25.6% HLA-A or HLA-B risk allele carriers), DPD deficiency-linked fluorouracil toxicity (1.4% DPYD intermediate or poor metabolizers) and malignant hyperthermia susceptibility due to potent volatile anaesthetic agents and succinylcholine (0.07% CACNA1S or RYR1 risk allele carriers). This evidence concerns the gene HLA-B and toxic epidermal necrolysis.