Understanding How Trim Builds Up in Your Body

When you begin Trim at the common starting dose of 2.5 mg once weekly, it’s important to understand that your body is gradually adapting to the medication. The effects don’t all happen at once - and the way the medicine accumulates in your system explains why.

What happens after each injection

After you inject Trim subcutaneously (under the skin), the active drug is absorbed into your bloodstream. The time to reach maximum concentration in your blood is typically 8 to 72 hours after the injection.

Its elimination half-life (the time for the concentration to drop by half) is about 5 days.

Because you are injecting once each week, you don’t wait until the drug is completely cleared before the next dose. That means each week the new dose is added when there is still drug present from the prior injection.

The “stacking” or accumulation effect

With each weekly injection, some of the drug remains in your system from previous injections. Because the half-life is roughly 5 days and the dosing interval is 7 days, the levels gradually rise over the first few weeks until they approach what’s called steady state.

“Steady state” means the amount of drug you take each week equals the amount your body clears between doses, so the concentration stabilises. For tirzepatide, steady state is generally achieved after about 4 weeks of consistent weekly dosing.

So in week 1 you start with a clean baseline. In week 2, there’s still carry-over from week 1. By week 4 you’re getting close to the plateau where each weekly dose adds less incremental rise because the system has built up.

Why you might not “feel” big changes right away

Because the drug concentration is still rising and your body is adapting, the early weeks may produce subtle effects rather than dramatic ones.

Effects such as improved appetite control, slowed gastric emptying (which keeps you feeling full between meals), improved blood sugar control or weight change tend to become more noticeable after the body has reached or approached steady state, and/or when higher maintenance doses are reached.

Also, the initial dose of 2.5 mg is a “starter” dose in many protocols (used for about 4 weeks) to build tolerance (especially to reduce gastrointestinal side-effects) before increasing.

So it’s entirely normal if you don’t feel major changes in your first week or two.

What this means for you

Stay consistent: taking your injection each week, on the same day/time, helps the accumulation and steady state process run smoothly.

Give it time: know that the major shifts in how you feel (like appetite control, energy levels, blood sugar stability or weight changes) often come after several weeks, not just days.

Stay on the starter dose for at least 4 weeks: don’t be too quick to escalate to a higher dose - remain on each dose for at least 4 weeks to ensure your body has time to adapt.

Have realistic expectations: the benefit builds over time. The first phase is more about laying the groundwork than experiencing full-effect.

Bottom line

Even though you inject once a week, Trim is not a one-and-done effect each week. The drug builds in your body across weeks until it reaches a steady cycle of effect. Because of that, it’s perfectly normal not to “feel” much immediately—but that doesn’t mean the medicine isn’t working. It means you’re in the foundation-building phase.

Further reading you might like:

Therapeutic Goods Administration (TGA). (2024, September). Australian public assessment report for tirzepatide (Mounjaro). Government of Australia. https://www.tga.gov.au/sites/default/files/2024-09/auspar-mounjaro-240920-pi.pdf

→ Australia’s official evaluation provides verified data on tirzepatide’s pharmacology, dose escalation schedule, and rationale for the 2.5 mg starting dose.U.S. Food and Drug Administration (FDA). (2022). Mounjaro (tirzepatide) injection, for subcutaneous use: U.S. prescribing information. Eli Lilly and Company. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/215866s000lbl.pdf

→ The official FDA label includes detailed pharmacokinetic data (absorption time, half-life, steady state) and is the definitive source on tirzepatide’s accumulation profile.

Frias, J. P., Nauck, M. A., Van J. P., Kulich, K., Milicevic, Z., Urva, S., Milicevic, Z., & Haupt, A. (2021). Efficacy and safety of tirzepatide monotherapy versus semaglutide in patients with type 2 diabetes (SURPASS-2): A double-blind, randomised controlled trial. The Lancet, 398(10295), 583–598. https://doi.org/10.1016/S0140-6736(21)01324-6

→ Includes pharmacodynamic data and clinical response timing, showing how tirzepatide’s effects develop over weeks as steady state is reached.

Rosenstock, J., Wysham, C., Frias, J. P., Kaneko, S., Lee, C. J., & Milicevic, Z. (2021). Tirzepatide once weekly for the treatment of type 2 diabetes. New England Journal of Medicine, 385(6), 503–515. https://doi.org/10.1056/NEJMoa2107519

→ A pivotal NEJM trial describing tirzepatide’s dose-response relationship and pharmacokinetic accumulation over multiple weeks.

Urva, S., Coskun, T., & Haupt, A. (2022). Clinical pharmacokinetics and pharmacodynamics of the dual GIP and GLP-1 receptor agonist tirzepatide. Clinical Pharmacokinetics, 61(10), 1305–1321. https://doi.org/10.1007/s40262-022-01144-z

→ Peer-reviewed review article summarising how tirzepatide is absorbed, metabolised, and achieves steady state, with visual plasma-concentration curves and modelling data.