Teriparatide: what it treats, how to take it, side effects
Last updated September 3, 2026.
Teriparatide (brand name Forteo) is a daily self-injection that actually builds new bone, rather than just slowing bone loss. It is a synthetic fragment of parathyroid hormone, reserved for osteoporosis that is severe, fracturing, or failing other treatments.
What does it treat?
It treats osteoporosis in postmenopausal women and in men at high fracture risk, and osteoporosis caused by long-term steroid use. In the pivotal trial it cut new vertebral fracture risk by 65% versus placebo. It is usually the move after fractures on, or intolerance of, bisphosphonates, or when the starting fracture risk is very high.
How do you take it?
Inject 20 mcg under the skin of the thigh or abdomen once a day, at about the same time each day, using the prefilled pen. The pen lives in the refrigerator (never the freezer), comes out only for the injection, and is discarded after 28 days even if medicine remains. Take the first few doses somewhere you can sit or lie down, because brief dizziness can follow. Lifetime use is capped at 2 years unless fracture risk stays high, because of a theoretical bone-cancer signal from rat studies. Missed dose: inject when you remember that day; if the day has passed, skip it; never two doses in one day.
Side effects to know
- Common: nausea, leg cramps, dizziness (especially early, on standing), joint aches, headache, and injection-site redness.
- Serious: high blood calcium, kidney stones, sustained orthostatic blood-pressure drops, and the reason for the 2-year cap: osteosarcoma seen in rat studies at high exposures, which is why it is avoided in anyone with elevated bone-turnover risk.
Who should not take it?
Avoid teriparatide if you have Paget's disease of bone, prior radiation to the skeleton, bone cancer or cancer spread to bone, unexplained high alkaline phosphatase, or high blood calcium, all situations where the osteosarcoma concern is amplified. It is not for children or for pregnancy. On digoxin, high calcium from any cause raises toxicity risk, so that combination gets watched.
When is it an emergency?
Call 911 for fainting that does not resolve on lying down, signs of severe allergic reaction (facial swelling, trouble breathing), or symptoms of very high calcium: severe nausea and vomiting, confusion, extreme thirst, or a racing irregular heartbeat. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why is there a 2-year lifetime limit?
Rats given high doses for most of their lives developed osteosarcoma, a bone cancer. No convincing human signal has emerged in over 20 years of use, but the cap stays as a precaution: more than 2 years total only if you remain at high fracture risk, and the drug is avoided entirely in people with bone-risk conditions like Paget's disease or prior bone radiation.
Do the injections hurt?
The needle is very fine, similar to an insulin pen, and most people rate it as a brief pinch. The daily rhythm matters more than the sting: same time each day, abdomen or thigh, rotating spots, pen back in the refrigerator immediately after.
How is teriparatide different from bisphosphonates?
Opposite mechanism. Bisphosphonates slow the cells that remove old bone; teriparatide stimulates the cells that build new bone. That anabolic action is why it is chosen when bone is already fracturing, and why treatment sequences matter: it often comes first, with an antiresorptive after to lock in gains.
What happens after the 2 years are up?
You switch to an antiresorptive like a bisphosphonate or denosumab. Teriparatide's new bone needs a follow-on drug to hold, since stopping without one lets the gains erode. The two-phase plan is usually mapped at the start, not figured out at month 23.
Does it need to be refrigerated?
Yes, always. The pen is stored in the refrigerator, never frozen, taken out only for the moment of injection, and thrown out 28 days after first use even if solution remains. Heat and freezing both wreck it, so travel needs a cooler plan.
Why did I feel dizzy after my first doses?
Teriparatide can briefly drop blood pressure on standing, mostly in the first doses. The label advises injecting somewhere you can sit or lie down right away. It typically fades as your body adjusts; persistent or worsening dizziness, or actual fainting, gets reported.