The Medicines and Healthcare products Regulatory Agency (MHRA) has warned that patients of Han Chinese or Thai origin who take Carbamazepine can be susceptible to "Stevens-Johnson Syndrome" if found to have the HLA-B* allelle present in their genetic profile. For this reason, the MHRA recommends that patients of these ethnic origins should not be treated with Carbamazepine unless they have been screened and found negative for the HLA-B* allelle.