Replace: give back what is missing
When a gland fails, the cleanest fix is to put the hormone back. Hormone replacement therapy aims to restore the body's natural set point using a manufactured copy of the missing molecule. The model case is hypothyroidism treated with levothyroxine, a synthetic version of thyroxine (T4). Taken once a day, it is converted by the body to active hormone, and the dose is tuned not by guesswork but by checking whether feedback has settled — when TSH returns to normal, the dose is right.
The same logic drives insulin therapy in type 1 diabetes, where the beta cells are gone and insulin must be injected to survive, and glucocorticoid therapy in Addison's disease, where lost cortisol is replaced. Replacement is conceptually simple but demands respect: too little leaves the deficiency, too much creates the opposite disease. The whole art is reading feedback to land on the set point.
Block: turn down an excess
When a hormone is in excess, the goal flips: turn the signal down. Drugs can do this at several points. An antithyroid drug blocks the very synthesis of thyroid hormone, calming an overactive gland in hyperthyroidism. A somatostatin analog mimics the body's own “stop” signal to silence a hormone-secreting pituitary tumor in acromegaly. Other drugs block the receptor so the hormone arrives but cannot be heard.
A subtle and powerful tool is the GnRH analog. Given in a steady stream rather than the body's natural pulses, it paradoxically shuts down the gonadal axis — the constant signal exhausts and silences the pituitary, lowering sex hormones. This counter-intuitive trick treats prostate cancer, endometriosis, and precocious puberty, and shows how deeply treatment depends on understanding the rhythm of negative feedback.
Remove: when surgery is the answer
Sometimes the cleanest cure is to take out the source. A functional tumor pouring out hormone — a pheochromocytoma, a prolactinoma that resists drugs, an aldosterone-producing adrenal nodule — is often cured by surgery once it has been localized by imaging and pinned down biochemically. Removing one overactive parathyroid gland can fix hyperparathyroidism in a single operation.
- Confirm the excess biochemically with a hormone assay and, where needed, a suppression test — never operate on a picture alone.
- Localize the source with the right scan so the surgeon knows exactly what to remove.
- Plan for after: removing a gland may create a deficiency, so replacement therapy often follows surgery.
Removal trades one problem for another and then solves it: take out a thyroid for cancer or severe Graves' disease, and the patient will need lifelong levothyroxine afterward. That is not a failure — it is the same three moves working together. Across all of endocrinology, treatment is just replace, block, or remove, each aimed at restoring a feedback loop to its rightful balance.