How stacked doses combine

Most users dose more than once a week. Many stack multiple compounds. The dashboard's curves combine these correctly — this page explains how.

Same compound, multiple doses

If you dose Tirzepatide weekly, you have many doses overlapping over the course of a month. Each dose contributes its own Bateman curve (rise → peak → exponential decay). The active-amount curve at any moment is the sum of every dose's contribution at that moment.

       Dose 1 alone:   ▁▃▆█▆▅▄▃▂▁
       Dose 2 alone:           ▁▃▆█▆▅▄▃▂▁
       Sum:            ▁▃▆█▆▆▇█▇▆▅▄▃▂▁
                       ↑       ↑
                       Dose 1  Dose 2

This is mathematically correct. Pharmacokinetics is linear at therapeutic doses — two simultaneous doses produce the additive sum, not some squared or saturated combination.

Build-up to steady state

For weekly compounds with ~5-day half-lives, the trough of each dose is still ~50% of the peak when the next dose lands. Over several weeks, the trough rises until peak and trough stabilize:

• Week 1: peak X, trough ~0.5X.
• Week 2: peak ~1.5X, trough ~0.75X.
• Week 3: peak ~1.75X, trough ~0.875X.
• ...
• Steady state: peak ~2X, trough ~X.

The dashboard's PK curve shows this build-up. If you started Tirzepatide three weeks ago, you're still climbing toward steady state. By week 5–6, you're stable.

Different compounds (independent curves)

Doses of different compounds don't combine in the active-amount math. Each compound gets its own curve. If you take both Tirzepatide and Retatrutide, the dashboard plots two separate curves, each summing only its own doses.

Tirzepatide:  ▁▃▆█▆▅▄▃▂▁
Retatrutide:  ▁▃▆█▆▅▄▃▂▁
              (two separate lines on the chart)

The two curves don't get added together because they represent different molecules. Adding them would be a category error.

What does combine: receptor effects

Two compounds that hit the same receptor (e.g., Tirzepatide and Retatrutide both activate GLP-1R) produce a combined receptor effect, even though their molecules are tracked separately.

That combined effect is what the endogenous biomarker simulation computes. The simulation knows:

• Tirzepatide's affinity for GLP-1R, GIPR.
• Retatrutide's affinity for GLP-1R, GIPR, glucagon receptor.
• How much of each is currently in your system (from the PK curves).
• Combined receptor occupancy at any moment.

So the dashboard shows two separate active-amount curves, but the simulated downstream effects (insulin response, glucose disposal, satiety) reflect the combined receptor activation.

What about same-day multiple doses?

Some users split a weekly dose across days (e.g., half-Monday, half-Thursday) to smooth the peak. The math handles this fine — each half-dose is its own Bateman curve, and the sum is two smaller waves instead of one big one.

For daily peptides with very short half-lives (BPC-157, Tesamorelin), multiple doses per day are normal. Same math: each dose adds its curve.

Stacked custom + canonical

You can mix custom and canonical compounds. Canonical compounds (Tirzepatide, etc.) are in the simulation engine; custom compounds aren't. So:

• PK curves: both plot independently on the dashboard.
• Simulation receptor effects: only canonical compounds contribute.
• Pattern insights: both participate (correlations between custom dose and weight, symptoms, etc. all work).

If you're stacking BPC-157 (custom) with Tirzepatide (canonical), the dashboard shows two curves. The simulation models Tirzepatide's effects on your hormones; BPC-157's effects aren't simulated (we'd need pharmacology metadata we don't have for generic peptides).

Practical implications

You can dose the same week as a previous one without "starting over." The previous dose is still partly active. The next one stacks.

Skipping a week means the curve declines for ~2 weeks before bottoming out. Skipping doesn't fully reset — at week 2 post-skip you're still at ~0.5x normal trough.

Switching compounds (e.g., Tirzep → Reta) creates a transition window. Your residual Tirzep curve continues for ~3 weeks while the new Reta curve builds up. The simulation models receptor occupancy across this transition correctly.

Compounded versions with the same active ingredient stack with the catalog version. If you use both prescription Tirzepatide and a compounded version, log both — the math is additive at the molecule level.

Common questions

"Should I see the combined active amount across all my GLP-1s?" The dashboard plots them separately by default — clearer for understanding individual contributions. The simulation handles the combined receptor effect downstream.

"What if I dose at different doses each week (titration)?" The math handles it. Week 1 at 2.5mg gives a smaller curve. Week 2 at 5mg gives a bigger curve overlapping the residual. You'll see the build-up clearly during titration.

"Why doesn't my curve match published PK studies?" Published curves usually show single-dose pharmacokinetics in healthy volunteers. Real-world stacked dosing produces accumulated curves that don't look like the textbook diagram. The math is the same; the visual is different.

"Is the math for stacked doses different from single-dose math?" No. Linear pharmacokinetics. The sum of two single-dose curves is the multi-dose curve.

Related

• How half-life curves work — single-dose math.
• Endogenous simulation — what receptor occupancy does.
• Kinetics shapes — bolus, sub-Q, depot.