WHO names three common medicines as cancer-causing; experts advise caution, not panic
The International Agency for Research on Cancer (IARC), the World Health Organisation’s (WHO) cancer research agency, has classified three widely used medicines as “carcinogenic to humans” (Group 1). These are hydrochlorothiazide, used to treat high blood pressure; voriconazole, an antifungal drug; and tacrolimus, an immunosuppressant given to organ transplant recipients.
The assessment, published as Volume 137 of the IARC Monographs, and earlier outlined in The Lancet Oncology, is based on sufficient evidence linking these drugs to certain types of cancer. However, experts stress that this classification identifies a hazard, not the actual risk at prescribed doses. They urge patients not to stop or change their medication without consulting a doctor, as these drugs treat serious, often life-threatening conditions.
IARC found that hydrochlorothiazide increases the risk of squamous cell skin carcinoma and lip cancer. Studies from Denmark and the United States showed higher rates of non-melanoma skin cancers among long-term users. The mechanism is phototoxicity: the drug makes the skin more sensitive to ultraviolet (UV) radiation, heightening the chance of DNA damage after sun exposure.
Voriconazole was also linked to squamous cell skin carcinoma, particularly in transplant recipients on prolonged therapy, through a similar phototoxic pathway. Tacrolimus, which suppresses the immune system to prevent transplant rejection, was linked to non-Hodgkin lymphoma and post-transplant lymphoproliferative disorder, with limited evidence for leukaemia and skin carcinoma. Its risk arises from weakened immunity, which reduces the body’s ability to clear abnormal cells.
All three medicines are on the WHO Model List of Essential Medicines and are prescribed to millions of people worldwide, including in India. Hydrochlorothiazide is a common first-line treatment for hypertension, voriconazole is used in immunocompromised patients, and tacrolimus underpins post-transplant care in many Indian hospitals.
Dr. Kabir Sardana, Director, Professor and Head of the Department of Dermatology at Atal Bihari Vajpayee Institute of Medical Sciences and Dr. Ram Manohar Lohia Hospital, said the classification is highly relevant to India, “particularly in rural areas, the Northeast, hilly and coastal regions, and among outdoor workers such as farmers who are exposed to high levels of ultraviolet radiation.” He also noted that voriconazole is “frequently prescribed without labelled indications, including for fungal skin infections caused by Trichophyton indotineae.”
Dr. Sardana welcomed measures to curb inappropriate prescribing, adding, “We cannot ignore these warnings in a country where irrational prescribing, over-the-counter availability, and poor adherence to ethical prescribing and dispensing practices remain significant challenges.”
Doctors recommend that patients on hydrochlorothiazide or voriconazole continue sun-protection measures, including using sunscreen, limiting UV exposure, and having periodic skin checks. Transplant patients on tacrolimus are already routinely monitored for skin cancers and lymphoproliferative disorders.
The IARC Monographs identify whether an agent can cause cancer under certain circumstances, but they do not assess real-world risk at therapeutic doses. The benefits of these medicines in managing severe conditions remain well established. The priority, experts say, is informed prescribing and vigilant monitoring, not abandoning treatments that save lives.
