@gently

Thanks for the correction @gently. Tymlos targets specific receptors on bone-forming cells to build bone mass. That cellular process doesn't change based on your size.

But, in a smaller body with a lower total blood and fluid volume, the standard dosage of 80 mcg results in a higher concentration in the blood transiently right after the injection. That temporary spike in concentration may trigger the cardiovascular side effects—like a sudden drop in blood pressure, lightheadedness, or a racing heart. So while the bone-building mechanism doesn't care about your weight, your circulatory system feels the peak concentration more intensely if you have a smaller frame.

Some comments on: "It seems to me that just the biology of having a larger kidney with more weight would be enough conviction that weight matters. Larger kidney, larger bladder, larger bones."

1. The Side Effects Happen Before the Kidneys Get Involved
The lightheadedness, drop in blood pressure, and palpitations that happen after a Tymlos injection occur within minutes—driven by the drug temporarily relaxing blood vessels as it circulates in the blood.The kidneys are responsible for filtering waste out of the blood over time, but they don't prevent or control that initial peak concentration in the bloodstream.
Furthermore, Tymlos is actually cleared from the body primarily via glomerular filtration, but its clearance rate does not require dose adjustments based on weight or kidney size.

2. Bone Size Doesn't Mean You Need a Different Dose. While a larger person does have a larger skeletal mass, Tymlos is an anabolic (bone-building) agent that works by binding to specific parathyroid hormone receptors on bone cells. Receptors don't "soak up" the drug like a sponge based on bone size. The 80 mcg flat dose is more than enough to saturate the targeted cellular pathways in anyone, regardless of whether they have a larger or smaller skeletal frame.

3. What Actually Matters: Fluid Volume, Not Organ Size. The real reason a smaller person feels the side effects more intensely comes down to total blood and extracellular fluid volume, not the physical size of their kidneys or bladder.