The Prophet ﷺ said: "In the black seed there is healing for every disease except as-sām," and as-sām is death (al-Bukhārī 5688; Muslim 2215). The scholars — including Ibn Ḥajar in Fatḥ al-Bārī and Ibn al-Qayyim in Zād al-Maʿād — explain that this is general wording intended in a restricted sense: black seed is a beneficial remedy, often as one ingredient combined with others, and its effect depends on the illness, the dosage, and the constitution of the patient, all by Allah's permission. So a Muslim may take black seed as a sunnah remedy with good expectation of Allah, but it is not a substitute for necessary medical treatment, and claiming it must heal every condition contradicts how the scholars of hadith understood the text.
Evidence — the daleel
Sahih al-Bukhari 5688 ṢaḥīḥSahih Muslim 2215 Ṣaḥīḥ
On deen2u
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.