What is the appropriate response to secularists who criticize Muslims regarding the narration about treating illnesses with camel urine, and how did the Prophet, peace and blessings be upon him, legitimize treating with such things?

The believer must affirm and submit to what has come from Allah and His Messenger. The authentic Sunnah cannot be rejected or objected to. The Messenger, peace and blessings be upon him, does not speak from his own inclination; what he brought is divine revelation, and in it is a cure for diseases. Among these is his guidance to treat with camel urine and milk, as proven in the Hadith of the 'Uraniyyin, where the Messenger commanded them to drink it for dropsy. Camel urine is pure and a beneficial medicine, and this has been proven by experience. Ibn Sina is among those who supported its medicinal benefits.