New Era Comb M contains calc phos, kali phos, nat phos and nat sulph. Calc phos is often linked with rebuilding and recovery, kali phos is commonly used for nerve-related discomfort and fatigue, nat phos is the tissue salt most associated with acid balance, and nat sulph is traditionally used when joints or tissues seem stiff and heavy, especially in damp conditions.
That gives New Era Comb M a broad rheumatic support role. It is usually chosen when aches are not just about sharp pain, but also about stiffness, heaviness or discomfort that is worse after certain foods or in certain weather. Biotin is included as an added nutrient, but the tissue salts do most of the explanatory work here.
Nat phos and nat sulph are often the important pair in products for this sort of symptom pattern. They are traditionally used where acidity, biliousness or damp-linked stiffness seem to sit in the background of the discomfort.