Tirzepatide Dosing Guide: mg, Units, and Microdosing Charts

Your prescription says mg. Your syringe says units. Nobody explains the gap — and that gap is where most dosing errors happen.

Tirzepatide comes from the pharmacy two ways. On Mounjaro or Zepbound, the pen is pre-filled and dose-specific — click and inject. With compounded tirzepatide from a vial, you draw the dose yourself using an insulin syringe marked in units. Same drug. Two completely different measurement systems. This guide closes that gap: the conversion tables, the full FDA titration schedule, what microdosing is and when it makes sense, and what the clinical data actually says about dose and outcomes.

If you're looking for a provider, we track weight-loss clinics in Houston, Miami, and Los Angeles with verified tirzepatide availability.

The FDA-approved titration schedule

The approved Zepbound prescribing label starts at 2.5 mg weekly for four weeks, then steps up by 2.5 mg every four weeks. The full sequence:

• Weeks 1–4: 2.5 mg
• Weeks 5–8: 5 mg
• Weeks 9–12: 7.5 mg
• Weeks 13–16: 10 mg
• Weeks 17–20: 12.5 mg
• Week 21 and beyond: 15 mg (maximum)

The SURMOUNT-1 trial published in the New England Journal of Medicine showed mean weight loss of 22.5% of body weight at 15 mg versus 16% at 5 mg over 72 weeks. Most patients reach their goal somewhere between 5–10 mg with fewer side effects. The 15 mg ceiling exists for people who need it — not because higher is always better.

The four-week interval is a minimum, not a deadline. The prescribing information explicitly permits slower progression. Treating the schedule as mandatory is the most common mistake providers see.

Unit conversion: mg to units

The conversion depends entirely on your vial's concentration. Confirm with your pharmacy before drawing anything — using the wrong concentration and getting the units "right" still means the wrong dose.

At 5 mg/mL:

• 2.5 mg = 50 units
• 5 mg = 100 units
• 7.5 mg = 150 units
• 10 mg = 200 units

At 10 mg/mL:

• 5 mg = 50 units
• 10 mg = 100 units
• 12.5 mg = 125 units
• 15 mg = 150 units

The formula: dose (mg) ÷ concentration (mg/mL) × 100 = units. Write it down and keep it next to the vial. At 5 mg/mL, a 5 mg dose is 100 units. At 10 mg/mL, that same 100 units would deliver 10 mg — a double dose. This is the exact error the unit system enables.

What to expect in the first four weeks

The 2.5 mg starting dose is deliberately low — it's a tolerance-building phase, not a therapeutic dose. Most people see minimal appetite suppression at this level. That's expected. The point is to let your GI system adjust before the drug starts working in earnest.

Side effects typically peak in the 48 hours after injection and taper off toward day six or seven. Nausea is the most common complaint — usually mild at 2.5 mg. If you want a detailed breakdown of what the side effect curve looks like week by week, see our guide on the GLP-1 side effects timeline.

Two things you can do in week one that compound across the full treatment: establish your injection day and time (same day each week), and start rotating sites immediately rather than waiting. Both habits are much harder to build after the fact. Curious about how long it takes GLP-1s to produce visible weight loss? The data is more specific than most people expect.

Microdosing tirzepatide: what it is and when to consider it

Microdosing means starting below 2.5 mg — typically 1–1.25 mg weekly for two to four weeks. It's not FDA-approved, but some providers use it off-label for patients who genuinely cannot tolerate standard starting doses.

Tirzepatide activates both GIP and GLP-1 receptors simultaneously. That dual action produces stronger appetite suppression than semaglutide alone — but it also hits harder on nausea in sensitive patients. A lower starting dose gives the GI system time to adapt before the first step up.

Calculating a 1.25 mg microdose:

• At 5 mg/mL: 1.25 ÷ 5 × 100 = 25 units
• At 10 mg/mL: 1.25 ÷ 10 × 100 = 12.5 units (round to 13)

This only works with compounded tirzepatide — pre-filled pens cannot be subdivided. You'll need a provider experienced with off-label GLP-1 prescribing. If you're looking for one, we list tirzepatide providers in San Antonio and other major metro areas with verified availability.

Injection technique

Subcutaneous means fatty tissue, not muscle. Three standard sites: abdomen (at least two inches from your navel), upper thigh, and outer upper arm. All work. Rotate weekly.

Injecting the same spot repeatedly causes lipohypertrophy — fatty deposits that form under the skin and alter how the drug absorbs. This isn't just uncomfortable; it makes your dose unpredictable over time.

Missed dose: fewer than four days late, inject immediately and resume your normal schedule. More than four days, skip that week and pick back up on your regular day. Never double-dose.

Storage: refrigerate pens and vials at 36–46°F. Opened compounded tirzepatide vials typically remain stable 28–56 days refrigerated depending on formulation. Confirm the specific window with your pharmacy — it varies.

When to slow down escalation

Pause at your current dose for another four weeks before stepping up if you experience any of these:

• Nausea that persists past the first few days after injection
• Vomiting more than twice in one week
• Losing more than three pounds in one week from reduced appetite alone

The most common mistake in GLP-1 therapy is pushing through severe side effects to reach a higher dose on schedule. Patients who escalate slowly enough to build new eating habits alongside reduced appetite do better long-term than those who race to maximum doses. This is consistent across both the SURMOUNT trial series and real-world prescribing data.

One specific note: if you're in perimenopause or using oral hormone replacement therapy, discuss tirzepatide timing with your provider before starting. GLP-1s delay gastric emptying, which affects how oral medications absorb — including oral estrogen and progesterone. We cover the full interaction picture in our guide on GLP-1 medications and HRT.

Tirzepatide vs. other GLP-1s on dosing complexity

Semaglutide (Ozempic, Wegovy) runs two dose steps over four months before maintenance. Tirzepatide has six steps — but that granularity is the point. Its dual-receptor activation creates a steeper dose-response curve, so small increases produce larger effects. The longer titration exists because the drug earns it.

Retatrutide — the next-generation triple agonist activating GIP, GLP-1, and glucagon receptors — is still in trials. Oral and sublingual GLP-1 formats are advancing, including tirzepatide tablets, but haven't yet matched injectable tirzepatide efficacy in head-to-head data.

Frequently asked questions

How do I convert tirzepatide mg to units?

Divide your dose in mg by the vial concentration in mg/mL, then multiply by 100. At 5 mg/mL, a 5 mg dose equals 100 units. At 10 mg/mL, a 5 mg dose equals 50 units. Always confirm your vial's concentration with your pharmacy before calculating — compounded tirzepatide comes in both concentrations and they are not interchangeable.

What is the starting dose for tirzepatide?

The FDA-approved starting dose is 2.5 mg once weekly for the first four weeks. This is a tolerance phase — most patients don't see significant appetite suppression at this level. The goal is GI adaptation, not immediate weight loss. After four weeks, the dose increases to 5 mg.

Can I start tirzepatide at a lower dose than 2.5 mg?

Yes, but only with compounded tirzepatide and a provider who prescribes off-label. Starting at 1–1.25 mg — sometimes called microdosing — is used for patients with severe GI sensitivity or a history of intolerable nausea on GLP-1s. It's not FDA-approved and requires a vial, not a pre-filled pen. See the microdosing section above for dose calculations.

How often do you inject tirzepatide?

Once weekly, on the same day each week. The timing within the day is flexible — morning or evening, with or without food. Consistency matters more than the specific time. Rotating your injection site each week is important; do not inject the same location two weeks in a row.

What happens if I miss a tirzepatide dose?

If fewer than four days have passed since your scheduled dose, inject as soon as you remember and resume your regular weekly schedule from that day. If more than four days have passed, skip the missed dose entirely and resume on your next scheduled day. Do not take two doses to compensate — tirzepatide's half-life is approximately five days, so doubling up creates a meaningful overdose risk.

Is 5 mg tirzepatide effective for weight loss?

Yes. The SURMOUNT-1 trial showed 16% mean body weight loss at 5 mg over 72 weeks — clinically significant and comparable to the highest approved semaglutide dose (2.4 mg Wegovy). Many patients maintain satisfactory, durable results at 5–7.5 mg without needing to escalate further. Higher doses produce greater average weight loss, but the marginal gain narrows and side effects increase. The right maintenance dose is the lowest one that achieves your clinical goal with manageable tolerability.