GLP-1 medicines explained: a beginner's guide for the Philippines

What GLP-1 medicines are

GLP-1 medicines are medicines that act on the receptor for GLP-1 (glucagon-like peptide-1), a natural hormone. The Wegovy and Zepbound labels describe GLP-1 as a physiological regulator of appetite and calorie intake.

A medicine that switches on a receptor is called a receptor agonist. This guide covers three medicines:

• Semaglutide is a GLP-1 receptor agonist. Its brands are Ozempic, Wegovy and Rybelsus.
• Tirzepatide is a dual GIP and GLP-1 receptor agonist. Its brands are Mounjaro and Zepbound.
• Retatrutide acts on three receptors: GIP, GLP-1 and glucagon. It is an investigational medicine and is not approved in any country in the sources checked.

Semaglutide and tirzepatide have approvals from regulators in the US and the EU. Ozempic, Wegovy, Rybelsus, Mounjaro and Mounjaro KwikPen are listed as registered in the FDA Philippines Verification Portal (see the table below).

How they work

Each medicine works a little differently, so the details below are given medicine by medicine.

Semaglutide

• It is a GLP-1 analogue with 94% sequence homology to human GLP-1, and it binds to and activates the GLP-1 receptor.
• It lowers blood sugar by increasing insulin release and lowering glucagon release, both only when blood sugar is raised. A small delay in stomach emptying after meals also contributes.
• The GLP-1 receptor is found in several brain areas involved in appetite. The Wegovy label says semaglutide lowers calorie intake, likely by affecting appetite.
• The European Medicines Agency describes it as increasing feelings of fullness while reducing food intake, hunger and cravings.
• It stays in the body a long time mainly because it binds to albumin, a blood protein, which slows its removal by the kidneys.

Tirzepatide

• It binds to and activates both the GIP and GLP-1 receptors, the targets of the body's own GIP and GLP-1 hormones.
• Both receptors are found in brain areas involved in appetite. Nonclinical studies (not in people) suggest GIP may add to the regulation of food intake.
• The Zepbound label says tirzepatide lowers calorie intake, likely by affecting appetite.
• The Mounjaro label says it increases insulin release and lowers glucagon levels, both only when blood sugar is raised. The Zepbound label says it also increases insulin sensitivity.
• It contains a fatty acid chain that binds to albumin, which prolongs how long it stays in the body.

Retatrutide (investigational)

• It is a single peptide that activates three hormone receptors: GIP, GLP-1 and glucagon.
• In clinical trials it is given as a once-weekly injection under the skin.

The medicines and their brands

Approvals differ by brand and by country. The Philippine status column shows what the FDA Philippines Verification Portal listed when it was searched on October 7, 2026. The portal records show registration and prescription status. The Philippine approved uses in the table come from the package inserts linked from those portal records, which apply to products registered in the Philippines.

The US FDA says Zepbound should not be used together with Mounjaro or a GLP-1 receptor agonist. The Wegovy label says using Wegovy with other semaglutide products or any other GLP-1 receptor agonist is not recommended.

What the main trials found

The tables below show the main published trials recorded for each medicine. Doses are the doses tested in each trial, not a guide to treatment. Each result applies to that trial's population, doses and length. Averages do not predict what any one person will experience.

Weight trials: semaglutide (STEP)

Weight trials: tirzepatide (SURMOUNT)

Weight trials: retatrutide (investigational, phase 3)

Retatrutide is not approved anywhere in the sources checked. The three retatrutide trials in the table above were all funded by Eli Lilly.

Trials of other outcomes

A few points help with reading these results:

• In STEP 1, 86.4% of people on semaglutide lost 5% or more of their body weight, compared with 31.5% on placebo. In SURMOUNT-1, 85%, 89% and 91% lost 5% or more on the three tirzepatide doses, compared with 35% on placebo.
• In SUSTAIN-6, rates of diabetic eye (retinopathy) complications were higher with semaglutide than with placebo (hazard ratio 1.76).
• SURPASS-2 and SURMOUNT-5 were open-label, which means participants knew which medicine they were taking.
• Which medicine fits a person is a decision for a doctor.

How fast they work and what happens if you stop

In the semaglutide and tirzepatide trials, weight loss started early and continued for more than a year. In the trials that stopped treatment, weight went back up.

How fast

• Semaglutide, STEP 1: the European Medicines Agency says weight loss started early and continued throughout the 68 weeks.
• Semaglutide, STEP 5: mean body weight went down until week 68 and then levelled off. With placebo, weight went down less and levelled off after about 20 weeks.
• Tirzepatide, SURMOUNT-1: in an analysis of 1,545 people taking tirzepatide, 82% had lost 5% or more of their weight by week 12. Of those who had not, 70% reached 5% by week 24 and 90% by week 72.
• Tirzepatide over 3 years: in SURMOUNT-1 participants with obesity and prediabetes, weight change at 176 weeks was -12.3%, -18.7% and -19.7% with tirzepatide 5 mg, 10 mg and 15 mg, versus -1.3% with placebo.
• Retatrutide (investigational), phase 2: in 338 adults with obesity or overweight, mean weight change at 24 weeks ranged from -7.2% to -17.5% across dose groups versus -1.6% with placebo, and at 48 weeks from -8.7% to -24.2% versus -2.1%.

What happens if you stop

The STEP 1 extension authors wrote that the findings suggest ongoing treatment is needed to keep the improvements in weight and health. In SURMOUNT-1 participants with prediabetes, 17 weeks after stopping tirzepatide, 2.4% had type 2 diabetes, versus 13.7% of those who had taken placebo.

No study on stopping retatrutide was recorded.

Muscle and fat

The question many people ask is whether the weight lost is fat or muscle. The studies recorded here measured fat mass and lean mass. They do not report muscle separately.

• Semaglutide: the Wegovy label says semaglutide lowers body weight with greater fat mass loss than lean mass loss. In a STEP 1 sub-study of 140 people using DEXA scans, the European Medicines Agency says the results suggest most of the weight lost was fat tissue, including visceral fat (fat around the organs).
• Semaglutide, STEP 6: in 401 adults from Japan and South Korea with obesity, visceral fat area measured by CT in a subset fell by 40.0% with semaglutide 2.4 mg versus 6.9% with placebo over 68 weeks.
• Tirzepatide: the Zepbound label says tirzepatide lowers body weight with greater fat mass loss than lean mass loss. In a SURMOUNT-1 DXA substudy of 160 people, at 72 weeks body weight changed by -21.3%, fat mass by -33.9% and lean mass by -10.9% with tirzepatide, versus -5.3%, -8.2% and -2.6% with placebo. About 75% of the weight lost was fat and 25% was lean mass, in both the tirzepatide and placebo groups.

No body composition data for retatrutide was recorded.

Side effects

The most common side effects on the US labels for semaglutide and tirzepatide are digestive. The table names the label each list comes from.

The Zepbound label says most nausea, vomiting and diarrhea happened while the dose was being increased and decreased over time.

Serious warnings on the US labels

• Thyroid tumors (boxed warning, Wegovy and Zepbound labels): semaglutide and tirzepatide caused thyroid C-cell tumors in rodents. It is unknown whether they cause these tumors, including medullary thyroid carcinoma (MTC), in humans.
• Pancreatitis (Wegovy and Zepbound labels): acute pancreatitis, including fatal cases, has been seen in patients treated with GLP-1 receptor agonists and with tirzepatide.
• Gallbladder disease (Wegovy and Zepbound labels): in the Wegovy adult weight trials, gallstones were reported in 1.6% of people on Wegovy versus 0.7% on placebo.
• Low blood sugar (Wegovy and Mounjaro labels): people who also take insulin or a sulfonylurea may have a higher risk of low blood sugar, including severe episodes.
• Kidney injury (Wegovy and Zepbound labels): dehydration from vomiting or diarrhea can lead to acute kidney injury.
• Eye problems in diabetes: the Wegovy label says diabetic retinopathy complications have been reported with semaglutide. The Zepbound label says temporary worsening of diabetic retinopathy has been reported with rapid improvement in blood sugar control.
• Allergic reactions (Ozempic and Zepbound labels): serious reactions such as anaphylaxis and angioedema have been reported.
• Surgery and sedation (Ozempic and Zepbound labels): pulmonary aspiration has been reported in patients on GLP-1 receptor agonists having general anesthesia or deep sedation. Tell your doctor about any planned surgery or procedure.
• Heart rate (Wegovy label): average resting heart rate rose by 1 to 4 beats per minute compared with placebo in adults in the weight trials.
• Other medicines: the Ozempic label says semaglutide slows stomach emptying and may affect how oral medicines are absorbed. The Zepbound label says tirzepatide may make birth control pills less effective, and advises a non-oral or added barrier method for 4 weeks after starting and after each dose increase.

For retatrutide, TRIUMPH-2 found low blood pressure in 1% to 6% of the retatrutide groups versus less than 1% with placebo, and dysesthesia in 4% to 7% versus 1%.

Who should not use them

The US labels name specific groups who should not use these medicines, or for whom they are not recommended.

• Thyroid cancer history (Wegovy and Zepbound labels): must not be used by people with a personal or family history of medullary thyroid carcinoma, or with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
• Serious allergy (Wegovy label): must not be used by people who had a serious allergic reaction to semaglutide or any ingredient.
• Severe gastroparesis (Ozempic and Zepbound labels): not recommended for people with severe gastroparesis (very slow stomach emptying).
• Pregnancy (Wegovy and Zepbound labels): both may cause harm to an unborn baby. The Wegovy label says to stop at least 2 months before a planned pregnancy because semaglutide stays in the body a long time. The Zepbound label says to stop when a pregnancy is recognized.
• Combining medicines: the Wegovy label says using it with other semaglutide products or any other GLP-1 receptor agonist is not recommended. The US FDA says Zepbound should not be used with Mounjaro or a GLP-1 receptor agonist.

Retatrutide is not approved, and Lilly says it is legally available only to participants in its clinical trials.

Injections and tablets

Most of these medicines are weekly injections under the skin. Semaglutide also comes as a daily tablet.

Rybelsus and Ozempic tablets are approved in the US for type 2 diabetes. How they are taken was not recorded for this page.

The Philippine package insert for Mounjaro KwikPen (linked from record DR-XY49504) says: "Each pre-filled KwikPen contains 2.4 ml of solution for injection (4 doses of 0.6 ml)."

The Ozempic and Mounjaro labels say a pen must never be shared with another person, even if the needle is changed.

Storage

Storage rules differ between the Philippine package inserts and the US labels. The Philippine package insert applies to products registered in the Philippines.

Philippine package inserts (linked from FDA Philippines Verification Portal records)

US labels

The US labels allow an opened Ozempic pen or Wegovy FlexTouch pen to be kept for 56 days, while the Philippine inserts say 6 weeks. The US label allows an opened Mounjaro KwikPen to be kept in the refrigerator or at room temperature, while the Philippine insert says to keep it unrefrigerated below 30 °C.

None of these injections should be frozen or used if they have been frozen, according to the Ozempic, Wegovy, Mounjaro and Zepbound labels. The US FDA advises not using any injectable GLP-1 medicine that arrives warm or without enough refrigeration.

Dose schedules

Each brand's US label starts at a low dose and raises it step by step, to reduce the risk of digestive side effects. This is the label schedule, not personal advice. Your doctor sets your dose.

These schedules are for the branded medicines only. They are not schedules for compounded semaglutide or tirzepatide.

The Wegovy and Zepbound labels say to consider treatment response and tolerability when choosing the maintenance dose. The Wegovy label says that if a dose is not tolerated during the increase, delaying the next step by 4 weeks can be considered.

Investigational medicines: retatrutide

Retatrutide is an investigational medicine made by Eli Lilly. It is not approved for sale in any country in the sources checked.

• Approval status: Lilly describes it as "an investigational molecule that cannot be legally sold or marketed for human use." On September 29, 2026, Lilly said it plans to submit an application to the US FDA in the first quarter of 2027. A submission is a request for review, not an approval.
• US FDA: as of October 1, 2026, the US FDA says retatrutide is not a component of any FDA-approved drug and cannot be used in compounding under US federal law. It has warned companies that illegally sold retatrutide falsely labeled "for research purposes" or "not for human consumption".
• Company-reported results: two further phase 3 trials, TRIUMPH-3 and TRIUMPH-4, have been reported by Lilly in press releases but were not found in peer-reviewed journals when this page was written. In TRIUMPH-4 (445 adults with obesity or overweight and knee osteoarthritis, 68 weeks), Lilly reported weight change of -20.0% and -23.7% in two dose groups versus -4.6% with placebo.
• Side effects: in TRIUMPH-1, as reported by Lilly, nausea occurred in 28.6% to 42.4% of retatrutide groups versus 14.8% with placebo, and stopping because of side effects in 4.1% to 11.3% versus 4.9%.
• Philippine status: unverified. No record was found in an FDA Philippines Verification Portal search on October 7, 2026. FDA Philippines issued two advisories in September 2026 (Advisory No. 2026-1265 on September 16 and Advisory No. 2026-1392 on September 22) warning the public not to buy or use unregistered retatrutide products that have no Certificate of Product Registration. FDA Philippines said using them may expose people to health risks, including possible injury or harm.

No dosing information is given for retatrutide on this site. Read more on the retatrutide page.

Branded, compounded and unregistered products

Not every product sold under these medicine names is the same. There are three kinds.

Branded. Ozempic, Wegovy, Rybelsus, Mounjaro and Zepbound are the brand-name medicines. The label facts and the semaglutide and tirzepatide trial results on this page are for these medicines.

Compounded.

• Compounded semaglutide is not the same product as Ozempic, Wegovy or Rybelsus.
• Compounded tirzepatide is not the same product as Mounjaro or Zepbound.
• The trial results on this page are not results for compounded versions.

The US FDA has said the following about compounded versions. These statements apply to the US legal framework, not the Philippines:

• Compounded drugs are not FDA approved, so the agency does not review them before they are marketed. It says they "should only be used in patients whose medical needs cannot be met by an FDA-approved drug."
• As of May 31, 2026, it had received 990 reports of adverse events associated with compounded semaglutide and more than 730 associated with compounded tirzepatide, and says these are likely underreported.
• It received reports of adverse events, some requiring hospitalization, that may be linked to dosing errors with compounded injectable semaglutide.
• Semaglutide sodium and semaglutide acetate "are different active ingredients than are used in the approved drugs."
• As of April 1, 2026, "Tirzepatide and semaglutide do not currently appear on the 503B bulks list or on FDA's drug shortage list."

Unregistered and "research" products. The US FDA reports fraudulent compounded semaglutide and tirzepatide with false label information, counterfeit Ozempic, and products falsely labeled "for research purposes" or "not for human consumption".

In the Philippines, FDA Philippines has warned the public against unregistered tirzepatide products (Advisory No. 2026-0814, July 30, 2026, and Advisory No. 2026-1020, September 1, 2026) and unregistered retatrutide products (see above). No FDA Philippines statement specifically about compounded semaglutide or tirzepatide was found. Zuellig Pharma, the Philippine distributor of Mounjaro, has warned that illegally compounded tirzepatide carries risks such as improper dosing and possible contamination (BusinessWorld, April 2026).

Getting them legally in the Philippines

Ozempic, Wegovy, Rybelsus and Mounjaro are listed as registered prescription drugs in the FDA Philippines Verification Portal (checked October 7, 2026), so the legal route starts with a prescription.

1. A prescription. Under the Philippine Pharmacy Act (RA 10918, Sections 30 and 33), prescription medicines may be dispensed only with a valid prescription from a physician, dentist or veterinarian.
2. A licensed pharmacist. They may be dispensed only by a registered and licensed pharmacist.
3. A licensed outlet. Medicines may be sold to the public only through a retail drug outlet licensed by FDA Philippines.

In February 2024, FDA Philippines said it was concerned about Ozempic sold online without a prescription and was investigating online sellers. It asks the public to report prescription drugs sold illegally online to ereport@fda.gov.ph.

You can check a product's registration on the FDA Philippines verification portal at verification.fda.gov.ph.

Where to read more

• Semaglutide: Ozempic, Wegovy and Rybelsus in depth
• Tirzepatide: Mounjaro and Zepbound in depth
• Retatrutide: the investigational triple agonist
• Semaglutide vs tirzepatide: the evidence side by side
• Ozempic vs Mounjaro: the two brands compared
• Are peptides legal in the Philippines?: how Philippine rules apply