People with conditions such as HIV, TB and malaria should not rely on homeopathic treatments, the World Health Organization has warned.
The group Voice of Young Science Network has written to health ministers to set out the WHO view.
WHO TB experts said homeopathy had "no place" in treatment of the disease.
"Homeopathy does not protect people from, or treat, these diseases.
"When homeopathy stands in place of effective treatment, lives are lost."