To identify which of the listed hormones is not a steroid, their classifications must be understood:
- Cortisol: A glucocorticoid steroid hormone from the adrenal cortex, regulating stress, metabolism, and immune functions.
- Testosterone: An androgen steroid hormone primarily from the testes (males) and ovaries (females), defining male sex characteristics.
- Progesterone: A progestogen steroid hormone active in the menstrual cycle, pregnancy, and embryo development.
- Glucagon: A peptide hormone from the pancreas that elevates blood glucose by stimulating the liver to convert glycogen to glucose.
Based on these classifications, Glucagon is definitively not a steroid hormone. It is a peptide hormone, distinct in structure and synthesis from the other options.