Peptides · Weight loss
Weight loss peptide reconstitution calculators
Pick your peptide, enter your vial size and BAC water volume, and get the exact units to draw on a U-100 insulin syringe. No sign-up, no math at 6 a.m.
Semaglutide reconstitution calculator
0.25-2.4 mg weekly · Ozempic / Wegovy
GLP-1 agonist. 14.9% body weight loss at 68 weeks in STEP 1.
Tirzepatide reconstitution calculator
2.5-15 mg weekly · Mounjaro / Zepbound
Dual GIP/GLP-1. 20.9% weight loss at 72 weeks in SURMOUNT-1.
AOD-9604 dosage calculator
250-1000 mcg daily · HGH fragment 177-191
Failed its Phase IIb obesity trial. Calculator included for completeness.
MOTS-c reconstitution calculator
5-10 mg weekly · Mitochondrial peptide
AMPK activator. Metabolic health focus, no human weight loss RCTs.
How peptide reconstitution works
Weight loss peptides ship as a freeze-dried powder inside a glass vial. That powder is pure drug. It does nothing until you mix it with a liquid you can actually draw into a syringe. That liquid is bacteriostatic water, BAC water for short, which is sterile water with 0.9% benzyl alcohol added as a preservative so the vial stays safe across multiple doses.
You pick how much BAC water to add. More water, thinner solution, larger injection volumes. Less water, thicker solution, smaller injection volumes. The peptide mass stays the same. A 5 mg semaglutide vial plus 2 ml of BAC water gives you 2.5 mg per ml. A 10 mg tirzepatide vial plus 2 ml gives you 5 mg per ml.
Once you know the concentration, you convert your target dose to units. A U-100 insulin syringe has 100 units per ml, so 0.1 ml is 10 units. That is all the math is. The calculator does it for you and prints the unit number you draw up. Aim water down the side of the vial, swirl gently, do not shake, and keep the reconstituted vial in the fridge.
Choose your weight loss peptide
Semaglutide (Ozempic, Wegovy)
Semaglutide is a GLP-1 receptor agonist with a half-life of about 7 days, which is why you inject once a week. Dosing starts at 0.25 mg and titrates up through 0.5, 1.0, and 1.7 mg to a target of 2.4 mg weekly. Wegovy got FDA approval for obesity in 2021, and the STEP 1 trial showed 14.9% body weight loss at 68 weeks versus 2.4% for placebo.
Tirzepatide (Mounjaro, Zepbound)
Tirzepatide is a dual GIP/GLP-1 receptor agonist, half-life around 5 days. You start at 2.5 mg weekly and step through 5, 7.5, 10, and 12.5 mg to a max of 15 mg. SURMOUNT-1 reported about 20.9% weight loss at 72 weeks on the 15 mg dose. Zepbound was FDA approved for chronic weight management in 2023.
AOD-9604
AOD-9604 is a modified fragment of human growth hormone (residues 177-191) that was developed as an obesity drug and failed its pivotal Phase IIb trial with no statistically significant weight loss over placebo. It is not FDA approved for any indication. Studied doses run 250-1000 mcg daily. If your goal is fat loss, the evidence does not support this one.
MOTS-c
MOTS-c is a mitochondrial-derived peptide that activates AMPK, the same metabolic pathway hit by exercise and metformin. Every weight-loss result comes from mouse studies. No human RCTs exist. Think of it as a metabolic health peptide that gets marketed for weight loss, not a proven weight loss drug.
Semaglutide vs tirzepatide for weight loss
The short answer: tirzepatide wins on average. SURMOUNT-5 put the two drugs head to head in the same trial, and tirzepatide produced 20.2% body weight loss versus 13.7% for semaglutide. That is a 6.5 percentage point gap in favor of tirzepatide, and it lines up with what SURMOUNT-1 and STEP 1 each showed in isolation.
The mechanism explains most of it. Semaglutide hits the GLP-1 receptor. Tirzepatide hits GLP-1 and GIP, and the extra receptor appears to amplify appetite suppression and insulin response beyond what GLP-1 alone achieves. The cost is slightly more GI distress at higher doses, and a longer titration ladder to climb (five steps instead of four).
Averages hide individuals. Some people respond better to semaglutide. Some cannot tolerate tirzepatide's nausea at 10 mg or 12.5 mg. Cost and supply also matter. If semaglutide is what you can access and afford, 13.7% average weight loss is still a dramatic result. The best weight loss peptide is the one you can actually take every week without quitting.
Do not stack them. Both activate GLP-1 receptors. Combining them does not double your results, it doubles your side effects and raises the risk of pancreatitis and hypoglycemia. Pick one.
Understanding units, mg, and mcg
Doses get written in milligrams (mg) or micrograms (mcg). 1 mg equals 1000 mcg. A 0.25 mg semaglutide dose is the same as 250 mcg. A 2.5 mg tirzepatide dose is 2500 mcg. The numbers look different, the amount of drug is identical.
Units on a syringe are a volume, not a mass. A U-100 insulin syringe is calibrated so that 100 units equals 1 ml (1 cc). That means 10 units is 0.1 ml and 50 units is 0.5 ml. To convert a dose to units you need the concentration of your vial. If your semaglutide is reconstituted to 2.5 mg/ml, then 0.25 mg is 0.1 ml, which is 10 units. If you reconstituted the same vial to 5 mg/ml instead, the same 0.25 mg dose is only 5 units. Concentration changes, units change, drug amount stays the same. This is exactly the math the reconstitution calculator handles.
Frequently asked questions
Which peptide produces the most weight loss?
Tirzepatide. In the SURMOUNT-5 head-to-head trial, tirzepatide produced 20.2% body weight loss versus 13.7% for semaglutide. SURMOUNT-1 on tirzepatide alone showed ~20.9% at 15 mg over 72 weeks. Semaglutide still produces dramatic results (~14.9% in STEP 1), it just loses the head-to-head.
How do I mix compounded semaglutide?
A common setup: 5 mg vial plus 2 ml of bacteriostatic water gives you 2.5 mg/ml. At that concentration, 0.25 mg is 10 units on a U-100 insulin syringe, 0.5 mg is 20 units, 1.0 mg is 40 units, and 2.4 mg is 96 units. Our semaglutide calculator does the math for any vial size and BAC water volume you have.
Can I stack semaglutide and tirzepatide?
No. Both activate GLP-1 receptors, and stacking them causes severe nausea and vomiting, raises pancreatitis risk, and can trigger dangerous hypoglycemia if you are also on insulin or a sulfonylurea. Pick one. If you want to switch from semaglutide to tirzepatide, stop the first before starting the second and work with a clinician.
What is bacteriostatic water and why does it matter?
Bacteriostatic water is sterile water with 0.9% benzyl alcohol, which stops bacterial growth once you start pulling doses from a vial. Plain sterile water has no preservative, so a multi-dose vial is unsafe with it. For any weight loss peptide you plan to inject across several weeks, use BAC water.
How many units do I draw on an insulin syringe?
Units depend on concentration, not mg. On a U-100 syringe, 100 units equals 1 ml. If your vial is 2.5 mg/ml, then 0.25 mg equals 0.1 ml or 10 units. If your vial is 5 mg/ml, the same 0.25 mg dose is 5 units. Double the concentration, half the units. Use the calculator to avoid doing this math at 6 a.m. half asleep.
Does AOD-9604 actually work for weight loss?
The clinical data says no. AOD-9604 failed its pivotal Phase IIb obesity trial with no statistically significant weight loss versus placebo. It is sold in research and anti-aging circles for fat metabolism claims, but the human evidence for weight loss is weak. Semaglutide and tirzepatide have real trial data. AOD-9604 does not.
Is MOTS-c a weight loss peptide?
Not really. MOTS-c is a mitochondrial-derived peptide that activates AMPK, and the weight-loss results come from mouse studies. There are no human weight-loss RCTs. It belongs in the metabolic health bucket, not the GLP-1 bucket. If fat loss is your only goal, start with a drug that has human trial data behind it.
How long does reconstituted semaglutide last in the fridge?
About 28 days refrigerated at 2-8 C once you reconstitute it with bacteriostatic water. Keep it upright, out of light, and do not freeze it. If you notice cloudiness, particles, or discoloration, throw the vial out.
Safety
Semaglutide and tirzepatide carry a boxed warning for medullary thyroid C-cell tumors based on rodent studies. Anyone with a personal or family history of medullary thyroid carcinoma or MEN2 should not take either drug. Watch for severe, persistent abdominal pain radiating to the back (possible pancreatitis) and stop dosing if it happens. Common side effects are nausea, vomiting, diarrhea, and constipation, usually worst during titration. Never combine semaglutide with tirzepatide. Read the full disclaimer.
This page is not medical advice. Semaglutide and tirzepatide are prescription drugs. Work with a qualified clinician before you start, adjust, or stop any peptide protocol.