What is GLP-1? A doctor explains the difference between oral medication and injections.
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June 16, 2026
What is GLP-1? A Doctor Explains the Difference Between Oral and Injectable Medications
A Doctor Explains How to Choose What's Right for You
"I often hear about GLP-1, but what is it?" "What's the difference between oral and injectable medications?" "Which is better for me, Rybelsus or Mounjaro?" While interest in GLP-1 receptor agonists is rapidly growing, many people find it difficult to understand the different types and their distinctions.
GLP-1 receptor agonists are drugs that work on three fronts: appetite suppression, blood sugar control, and weight reduction. Originally developed as a treatment for type 2 diabetes, they have garnered attention as a medical weight loss solution due to their powerful weight loss effects.
In this article, a doctor from Mona Aoyama Clinic explains what GLP-1 is, the differences between oral and injectable medications, a comparison of representative drugs, their side effects, and the process for online prescription at our clinic.
- Online prescriptions for GLP-1 oral medication (Rybelsus) available nationwide
- Mounjaro (tirzepatide) also supported. Same-day prescription and shipping
- Support includes diet and exercise guidance
What is GLP-1?
GLP-1 (Glucagon-Like Peptide-1) is a hormone secreted from the intestines after eating. It promotes insulin secretion, suppresses glucagon, and slows gastric emptying to lower blood sugar levels, and also acts on the brain's appetite center to prolong feelings of fullness.
GLP-1 receptor agonists are drugs that mimic the action of GLP-1, designed to be broken down more slowly in the body and thus have a longer-lasting effect.
| Main actions of GLP-1 | Effect on diet |
|---|---|
| Promotes insulin secretion | Suppresses sharp rises in blood sugar and reduces fat accumulation |
| Slows gastric emptying | Longer-lasting satiety after meals, preventing overeating |
| Acts on the brain's appetite center | Appetite itself decreases. Food intake naturally reduces |
| Weight loss effect | Some drugs have shown a weight reduction of 5-15% or more in clinical trials |
Oral (Ingested) vs. Injectable — What's the Difference?
| Comparison Item | Oral Medication (Rybelsus) | Injection (Mounjaro, Ozempic, etc.) |
|---|---|---|
| Administration Method | One tablet daily, immediately upon waking | Weekly self-injection (subcutaneous) |
| Needle Resistance | ◎ No needles | △ Requires self-injection (thin needle, minimal pain) |
| Ingestion Restrictions | △ Must take immediately upon waking, with water only, no food/drink for 30 minutes | ◎ Few restrictions |
| Weight Loss Effect | ○ Approx. 3-5% (depending on dosage) | ◎ Approx. 10-20% (for Mounjaro) |
| Absorption Rate | △ Low absorption rate orally (approx. 1%) | ◎ High absorption rate via subcutaneous injection |
| Cost | ○ Relatively affordable | △ Slightly higher |
| Recommended for | Those who dislike needles, want to try it first, or prefer a gradual effect | Those seeking stronger effects or preferring weekly management |
💡 There is no single "right" answer. Rybelsus (oral medication) is easier for those who dislike needles or are trying GLP-1 for the first time, while Mounjaro (injection) is suitable for those seeking stronger weight loss effects. Both are available at our clinic.
Comparison of Major GLP-1 Drugs
| Drug Name | Type | Active Ingredient | Frequency of Administration | Estimated Weight Loss Effect | Available at our Clinic |
|---|---|---|---|---|---|
| Rybelsus | Oral Medication | Semaglutide | Once daily | Approx. 3-5% | ✅ Online prescription |
| Mounjaro | Injection | Tirzepatide (GLP-1 + GIP) | Once weekly | Approx. 15-20% | ✅ Online prescription |
| Ozempic | Injection | Semaglutide | Once weekly | Approx. 10-15% | To be confirmed |
| Victoza | Injection | Liraglutide | Once daily | Approx. 5-8% | To be confirmed |
Mounjaro (tirzepatide) is a "dual agonist" that acts on both GLP-1 and GIP (glucose-dependent insulinotropic polypeptide) receptors, making it one of the drugs currently known to have the most significant weight loss effect.
Side Effects of GLP-1
| Side Effect | Frequency | Management |
|---|---|---|
| Nausea/Vomiting | Most common (especially at the start) | Start with a small dose and increase gradually. Reduce meal portions. |
| Diarrhea/Constipation | Relatively common | Increase fluid intake and fiber. Often resolves within a few weeks. |
| Loss of Appetite | Common (also a treatment goal) | Pay attention to diet to avoid nutritional deficiencies. |
| Headache/Fatigue | Rare | Usually temporary. Consult a doctor if symptoms are severe. |
| Hypoglycemia | Rare when used alone | Caution when used with other diabetes medications. |
⚠️ Cannot be used by individuals with a history of pancreatitis or gallbladder disease, or during pregnancy/breastfeeding. Please disclose your medical history during the pre-prescription consultation.
Our Prescription Process
- Online Medical QuestionnaireEnter your height, weight, medical history, medications, and weight loss goals.
- Doctor's Review and ConsultationThe doctor will assess your eligibility for a prescription based on your questionnaire. They will suggest the type and dosage of medication.
- Prescription and PaymentPayments made by 4 PM will be shipped the same day.
- Start Medication and Follow-upInstructions for use and precautions will be provided. Follow-up support will be available via LINE regarding your progress.
Frequently Asked Questions
Rybelsus (oral medication) is recommended for those who dislike needles or want to try GLP-1 for the first time. Mounjaro is suitable for those seeking stronger weight loss effects or who prefer weekly management. During your consultation, we can suggest a plan tailored to your target weight and lifestyle.
Many people notice changes in appetite within 1-2 weeks, and changes in weight typically begin to appear within 1-2 months. A 5% reduction in body weight can be expected with 3-6 months of continuous use. Individual results may vary.
There is a risk of rebound after discontinuing the medication. While taking the medication, establishing healthy eating and exercise habits is key to long-term maintenance. Our clinic also provides advice on lifestyle habits.
Prescriptions for medical weight loss purposes are considered self-pay (not covered by insurance). While treatment for type 2 diabetes may be covered by insurance, our clinic's weight loss prescriptions are self-pay.
Related Columns
A Doctor Explains the Effects, How to Take, and Side Effects of Rybelsus (Oral Semaglutide) Mounjaro (Tirzepatide): Effects, Side Effects, and Who It's For Want to Lose Weight by Summer? A Comparison of GLP-1 and Fat-Dissolving InjectionsClinic Hours and Access (Online Consultation)
| Clinic Name | Mona Aoyama Clinic |
| Consultation Format | Online Consultation (nationwide) / In-person Consultation (Tokyo, Aoyama) |
| Location | D Building 3F, 1-10-3 Minami Aoyama, Minato-ku, Tokyo 107-0062 |
| Nearest Station | 5-minute walk from "Aoyama-itchome Station" on Tokyo Metro |
| Online Consultation | Available 24 hours / Same-day shipping (for payments by 4 PM) |
Consult Mona Aoyama Clinic for Medical Weight Loss
Online prescriptions for Rybelsus and Mounjaro available nationwide. Same-day prescription and shipping.