Foundayo is a once-daily tablet containing orforglipron, a small-molecule GLP-1 receptor agonist with no food or water restrictions. Mounjaro is a once-weekly injection containing tirzepatide, a dual GIP and GLP-1 receptor agonist. In trial data, Mounjaro has shown considerably greater average weight loss at its highest dose (up to 22.5% at 72 weeks) than Foundayo has shown at its approved maximum dose (11.1% at 72 weeks) — though the two haven't been tested head-to-head, so this isn't a controlled comparison. The core practical trade-off is format and mechanism: a daily tablet with no dietary restrictions and a single hormone pathway, versus a weekly injection with a dual hormone pathway and generally higher average results in trials to date. Both are available to order now.
Mounjaro contains tirzepatide, a peptide that activates two separate gut hormone pathways — GIP and GLP-1 — which is part of why it's shown such strong average results in trials. As a peptide, it has to be injected, since it would be broken down by digestion if swallowed, requiring a specific manufacturing and delivery approach entirely different from a conventional tablet.
Foundayo contains orforglipron, a small, non-peptide molecule that activates the GLP-1 pathway alone. Because it's chemically different from a peptide, it survives digestion intact and can be taken as a tablet — and because it doesn't need the absorption-enhancing ingredient some other oral GLP-1 medicines require, it can be taken at any time of day, with or without food or water. For a deeper look at this mechanism, see our dedicated guide on how Foundayo works.
| Foundayo | Mounjaro | |
|---|---|---|
| Manufacturer | Eli Lilly | Eli Lilly |
| Format | Daily tablet | Weekly injection |
| Active ingredient | Orforglipron (small molecule) | Tirzepatide (peptide) |
| Mechanism | GLP-1 receptor agonist only | Dual GIP + GLP-1 receptor agonist |
| Food/water restriction | None — any time of day | None — no timing restriction around meals |
It's important to be upfront here: Foundayo and Mounjaro haven't been tested against each other in a head-to-head trial, so any comparison below is between two separate trials with different designs and populations — not a controlled, direct comparison.
| Foundayo (ATTAIN-1) | Mounjaro (SURMOUNT-1) | |
|---|---|---|
| Trial duration | 72 weeks | 72 weeks |
| Average weight loss (highest dose) | 11.1% | ~22.5% |
| Placebo group | 2.1% | ~2% |
On these figures, Mounjaro's trial showed a considerably larger average effect. It's worth noting Foundayo's dual authorisation also covers type 2 diabetes, and its ACHIEVE trial programme in that population has shown it outperforming oral semaglutide head-to-head — see our dedicated guide on Foundayo and type 2 diabetes for that separate, and genuinely strong, evidence base. For weight management specifically, though, trial averages currently favour Mounjaro.
| Foundayo | Mounjaro | |
|---|---|---|
| Starting dose | 0.8mg | 2.5mg |
| Number of steps | 6 | 6 |
| Minimum time per step | 30 days | 28 days (4 weeks) |
| Maximum dose | 17.2mg | 15mg |
Both follow a similar overall timeline of around five months to reach their respective maximum doses. For the complete schedules, see our dedicated Foundayo dosage guide and Mounjaro dose schedule guide.
Side Effects ComparedBoth share a broadly similar gastrointestinal side-effect profile — nausea, diarrhoea, vomiting, constipation and indigestion are the most commonly reported for both, particularly during dose escalation. Mounjaro's dual mechanism may produce slightly more pronounced early gastrointestinal effects for some people, though current evidence doesn't clearly establish one as consistently better tolerated than the other, and individual response varies considerably.
Important
Never combine Foundayo and Mounjaro, or take either alongside another GLP-1 receptor agonist medicine. If you're considering switching between them, this should always be planned with your prescriber, typically involving a washout period.
This is another genuine point of difference beyond mechanism. Mounjaro's injection pens must be refrigerated before first use and require careful handling — see our dedicated Mounjaro storage guide for the full 30-day rule once opened. Foundayo, as a tablet, needs no refrigeration at any point, making it considerably simpler to store, carry and travel with, without needing to think about cold-chain logistics at all.
Neither Foundayo nor Mounjaro currently holds a specific UK licence for cardiovascular risk reduction — that indication currently belongs to the Wegovy injection, based on the SELECT trial. Foundayo does have a dedicated cardiovascular outcomes trial underway (ATTAIN-Outcomes), including UK sites, so this picture may change as more data becomes available. If cardiovascular risk reduction specifically is a priority for you, it's worth discussing all the available options, including Wegovy, with your prescriber rather than assuming either Lilly product covers this.
A Genuinely Different Choice From the Same CompanyIt's worth appreciating why Lilly has developed two such different products rather than just one. Some people will always prefer, or medically require, a tablet over an injection — needle phobia is a genuine and common barrier that stops people starting treatment altogether. Others prioritise the strongest possible average result and are comfortable with a weekly injection to get it. By offering both a dual-mechanism injection and a single-pathway tablet, Lilly is addressing two different patient priorities rather than simply iterating on one product — which is exactly why this comparison isn't really about which medicine is "better" in the abstract, but which trade-offs matter more to you.
Which Might Suit You BetterFoundayo may suit you if…
- You have needle anxiety or would simply prefer never to self-inject
- You want a treatment with no fasting or food-timing requirement at all
- You want to start treatment today — Foundayo is available to order now
Mounjaro may suit you if…
- Maximum average weight loss, based on current trial data, is your top priority
- You're comfortable with a weekly injection rather than a daily tablet
- You'd prefer a medicine with a longer UK real-world track record
If you start on one and want to move to the other, this is possible but needs proper planning with your prescriber — you won't simply carry over your current dose, since the two work through different mechanisms with no established dose equivalence. Lilly's own ATTAIN-MAINTAIN trial has specifically studied switching from injectable tirzepatide to Foundayo tablets, finding that people generally maintained their previously achieved weight loss after switching.
Both Available Now — Find the Right One for You
Whether you're drawn to Foundayo's tablet format or Mounjaro's stronger average trial results, both are available to order through Happy Pharmacy following a free online consultation.
Start Your Free Online Consultation → Use code SWITCH10 if you're switching from another providerHappy Pharmacy is a GPhC-registered pharmacy (No. 9012585) — Superintendent Pharmacist: Palvinder Deol — Rated 4.8★ Excellent on Trustpilot
- Foundayo® (orforglipron) Summary of Product Characteristics, MHRA Products website.
- Mounjaro® (tirzepatide) UK Summary of Product Characteristics.
- Wharton S, et al. ATTAIN-1. N Engl J Med, September 2025.
- Jastreboff AM, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022.
- Orforglipron Maintains Weight Loss in Patients Switching from Semaglutide or Tirzepatide (ATTAIN-MAINTAIN). HCPLive, 2026.
- Eli Lilly and Company. Mounjaro® and Foundayo™ Prescribing Information, lilly.com.
- MHRA. UK first in Europe to authorise orforglipron for weight management and type 2 diabetes, 10 August 2026.