Teriparatide

Structure: The first 34 amino acids of the 84 amino acid human parathyroid hormone, produced recombinantly. This N-terminal fragment carries the full receptor-activating activity of the intact hormone. This is an approved prescription medicine with a real regulatory file behind it, not a research chemical, which puts it in a different evidentiary category from most compounds on this list.

Dosage:

• Standard: 20mcg SubQ once daily, delivered from a multi-dose prefilled pen. This is the approved dose for osteoporosis and there is no established reason to exceed it.
• Duration: courses of 18 to 24 months. The original label carried a 24 month lifetime limit; that restriction was removed in 2020, but treatment is still finite because the anabolic response attenuates over time.
• After stopping: the bone gained is lost fairly quickly unless followed by an antiresorptive agent. Coming off teriparatide without a follow-on plan wastes the course.

Administration:

• SubQ into the thigh or abdomen, once daily, using the supplied pen
• Take it at the same time each day, and take the first few doses sitting or lying down because of possible orthostatic hypotension
• Refrigerate. Teriparatide is a protein and heat-labile; a pen left out is a wasted pen
• Do not split, cycle, or pulse it in a non-daily pattern. The daily-intermittent pattern is the mechanism

Key Notes:

• Intermittent versus continuous is the whole pharmacology. A once-daily spike of PTH stimulates osteoblasts and produces net bone formation. Continuously elevated PTH, as in hyperparathyroidism, stimulates osteoclasts and produces net bone loss. Same hormone, opposite outcomes, determined entirely by the exposure pattern. This is why the short half-life is a feature rather than a limitation, and why any attempt to make it "last longer" would invert the effect.
• Get the osteosarcoma story right. Teriparatide carried a boxed warning for osteosarcoma based on a rat carcinogenicity study, in which Fischer 344 rats given high doses for most of their lifespan developed bone tumours in a dose and duration dependent way. Rat bone biology is a poor model here: rats have continuously growing bone with growth plates that never close, unlike adult humans. After roughly 15 years of post-marketing surveillance failed to show an increased osteosarcoma signal in treated patients, the FDA removed both the boxed warning and the lifetime treatment limit in 2020. The honest summary is that the warning came from rats, and human data did not confirm it. It is not that the concern was fabricated, and it is not that it remains an active clinical warning.
• Why this matters for enhanced athletes: bone is an under-monitored casualty of PED use. Years of aggressive aromatase inhibitor use crushing oestradiol, hard dieting, low body fat in female athletes, and repeated high-impact loading all degrade bone density, and the resulting stress fractures and poor healing usually get blamed on training. Oestradiol is the dominant regulator of bone in both sexes, which is why chronically suppressed E2 on cycle is a genuine skeletal risk rather than just a joint-pain complaint.
• Off-label fracture healing use is not well established. Teriparatide is used off-label for delayed union, non-union, atypical femoral fractures and pelvic fragility fractures, and there are positive small trials and case series. The evidence is suggestive, not conclusive, and it is not an approved indication. Do not expect it to rescue a fracture that needs surgical fixation.
• Contraindications are firm and worth reading: pre-existing hypercalcaemia, primary hyperparathyroidism, Paget's disease of bone, unexplained elevated alkaline phosphatase, prior external beam or implant radiation to the skeleton, bone metastases or a history of skeletal malignancy, and severe renal impairment. These are not paperwork; several of them describe situations where teriparatide would make things materially worse.
• This is a prescription drug with a legitimate supply chain. If bone density is your actual problem, the route through a clinician gets you the real product, a DEXA baseline, and a follow-on antiresorptive plan. A grey-market pen gets you none of those.
• Correct vitamin D and calcium status before starting. Treating with an anabolic bone agent while deficient in the substrate wastes the course.

Bloodwork Monitoring:

• Calcium: the central marker, and timing decides whether the number means anything. Teriparatide causes a transient calcium rise peaking 4 to 6 hours post-dose that returns to baseline by 16 to 24 hours. Always draw as a trough, immediately before the next dose. A sample taken mid-afternoon after a morning injection will show a physiological peak and send you chasing a problem that is not there. A persistently high trough calcium is the finding that matters and warrants stopping.
• Vitamin D: correct deficiency before starting and recheck during treatment. Teriparatide increases conversion to the active 1,25-dihydroxy form, and inadequate substrate limits the response.
• PTH: measure at baseline to exclude primary hyperparathyroidism, which is an absolute contraindication. Note that standard intact-PTH assays generally do not detect the 1-34 fragment, so an on-treatment result reflects your own suppressed endogenous PTH rather than the drug.
• ALP: rises during treatment as a marker of bone formation, and that rise is expected rather than alarming. An unexplained elevation before starting is a contraindication and needs investigating. A bone-specific ALP is more informative than total if your lab offers it.
• Phosphate: PTH promotes renal phosphate excretion, so a modest decline is expected.
• Uric Acid: teriparatide raises serum uric acid in a proportion of patients. Usually clinically silent, but relevant with a gout history.
• Creatinine and eGFR: baseline is required, since severe renal impairment is a contraindication and hypercalciuria raises kidney stone risk. If you have a stone history, a 24 hour urinary calcium is worth doing before starting.
• DEXA scan: not bloodwork, but it is the actual endpoint. Baseline before treatment and a repeat at 12 to 24 months, since no blood marker tells you whether the bone density improved.