Semaglutide and tirzepatide are two different active ingredients. Online they are often used almost interchangeably, as though they were two words for the same thing, and that is where a lot of confused paperwork begins. Writing the wrong one into a medicine list, a symptom diary, or a message to a clinic does not just lose a detail. It describes a medicine you are not taking.
This page is about that difference at the level of records: what each name refers to, which brands carry which ingredient, and what changes in the notes you keep. It does not compare how well either one works, because that comparison belongs to the clinician who knows your history, and nothing on this page is capable of standing in for that conversation.
What each name refers to
Semaglutide is an active ingredient that acts on GLP-1 receptors. Official labelling identifies it as the ingredient in Wegovy, which is licensed for weight management, and in Ozempic, which is licensed for type 2 diabetes. It does not arrive in only one form. It is supplied as an injection given once a week, and it is also supplied as tablets swallowed by mouth: labelling for the oral form now covers tablets under the Rybelsus and Ozempic names, and government drug information lists Wegovy among the brands under which semaglutide tablets are supplied. Three brand names, then, rather than the single tablet brand this ingredient had for years.
The practical consequence is that a brand name on its own no longer tells you how a medicine is taken. Only the pack in your hand and the prescription that produced it can do that, and a page like this one is not a substitute for either.
Tirzepatide is a separate active ingredient. Official Mounjaro labelling describes it as a GIP receptor and GLP-1 receptor agonist that binds to and activates both receptors, which is why it is usually discussed alongside GLP-1 medicines even though the more precise description names two pathways rather than one. Labelling identifies tirzepatide as the ingredient in Mounjaro and in Zepbound, both given as a weekly injection.
That is the whole of the difference as far as your records are concerned: two ingredient names, each attached to its own set of brand names, each with its own licensed uses and its own patient information leaflet. Nothing about being in the same conversation online makes them one substance.
Why the ingredient is what anchors a record
Brand names move around. They differ between countries, they change as licences are extended, and a pharmacy may dispense a name you have not seen before. The active ingredient is the more stable fact, which is why regulators and clinicians reach for it first, and why an accurate personal medication list is worth keeping in the form official guidance recommends: the name of the medicine, written as it appears on the label rather than as you remember it.
In practice the useful record carries both. The ingredient tells a clinician what the substance is. The brand tells them which licensed product, which device or pack, and which country's leaflet applies. Either one alone leaves a gap that someone will have to fill by asking you questions you may not remember the answer to.
What your tracking routine shares across the two
If your own pack is a weekly injection, most of the everyday recordkeeping looks the same whichever of these two ingredients is in the pen. You still note the day you injected and the day you meant to. You still note the general site used. You still record appetite, digestion, energy, and anything you would want a prescriber to hear about, dated at the time rather than reconstructed later. None of that changes with the ingredient, and there is no reason to rebuild a working log because the name on the box is different.
The symptom categories worth watching are also broadly shared. UK regulators have reminded patients and prescribers alike to stay aware of the possible side effects across this group of medicines, which is a reason to keep recording rather than a reason to expect any particular experience.
What genuinely changes
- The ingredient name you write down, and therefore the ingredient name you say out loud at an appointment
- Which patient information leaflet applies to you, since leaflets are written per product and not per class
- Which brand names are relevant when you are reading about other people's experiences, and which ones are simply about a different medicine
- Which forms exist at all: one of these ingredients is supplied as tablets as well as by injection, under several brand names, and the other is not
- Which regulator pages and official summaries are the right ones to check when you want a primary source rather than a forum post
Writing it down so it survives a year
- The ingredient name, spelled out in full, taken from the packaging rather than from memory
- The brand name exactly as printed on the dispensing label
- The date you started, and the date of any change your prescriber made
- The country the medicine was dispensed in, if you have ever been prescribed abroad
- Anything else you were taking at the same time, since a medicine list is far more useful to a clinician than a single line about one product
If a prescriber moves you from one to the other
This happens, and it is a clinical decision rather than a reader one. What is worth doing on your side is keeping the record clean across the change: close off the first entry with a date, open a new one, and resist the temptation to merge them into a single continuous line in a diary. A prescriber reading your notes later needs to see where one thing stopped and another began, particularly if a symptom pattern shifted around the same time.
It is also worth writing down what you were told the change was for, in your own words, on the day you were told. Weeks later that reasoning tends to blur into a general impression, and the general impression is the part least useful to whoever reviews you next.
What this page will not tell you
It will not tell you which ingredient is the right one for you, because that depends on your medical history, your other medicines, what your treatment is for, and factors no general page has access to. It gives no dose figures and no equivalence between the two, and there is a reason for the flat refusal: official UK guidance says these medicines vary in how strong they are and in the conditions they can be used for, and that switching without medical advice may increase the risk of experiencing side effects or make the treatment less effective. Conversion charts circulating online are exactly the thing that guidance is warning about.
If you are unsure which ingredient you have actually been prescribed, the fastest reliable answer is the label on the box or the leaflet inside it, and failing that, the pharmacy that dispensed it. If you are experiencing severe or rapidly worsening symptoms, that is not a records question at all, and urgent medical help is the right route rather than a diary entry.