How Many Units of Botox Are Needed for a Slimmer Face? A Comprehensive Analysis of Side Effects and Results of Botox Injections into the Chewing Muscles

Is Botox for a slimmer face suitable for everyone with a large face? In fact, a wide lower face may be caused by hypertrophied masseter muscles, fat accumulation, or bone structure. Since Botox primarily acts on muscles, it isn’t suitable for every face shape. This article summarizes the principles behind Botox for facial slimming, the dosage for the masseter muscle, common brands, side effects, and pre- and post-treatment precautions. It will help you understand the typical dosage in units (U) for Botox facial slimming and how to determine if it’s right for you.

Are You a Good Candidate for Masseter Botox? First, Take This Self-Assessment to Identify the Causes of a Large Face

A wide lower face isn’t necessarily caused by the masseter muscle. There are three common causes, each requiring a completely different treatment approach.

	Common Characteristics	The Benefits of Botox
Hypertrophy of the Masseter Muscle	When clenching the teeth, there is a noticeable bulge above the jaw angle; the face appears square when viewed from the front; and the person often grinds their teeth or has a habit of chewing on one side.	Suitable for
Fat Accumulation	When you're relaxed, your cheeks and jawline feel softer; when you gain weight, your face gets bigger.	Limited; must be used in conjunction with other methods
Skeletal Structure	A prominent mandibular angle is a condition in itself and has nothing to do with clenching or relaxing the jaw.	Since the bone structure cannot be changed, a doctor must evaluate other options.

What habits can lead to overdeveloped masseter muscles?

• Clenching your teeth for long periods: You unconsciously clench your teeth when you're focused on work or under a lot of stress.
• Nighttime teeth grinding: The masseter muscle remains tense during sleep, making it harder to notice than during the day.
• Preference for hard foods or frequent chewing of gum: Frequent chewing of gum or eating hard foods or foods that require prolonged chewing may increase the firmness of the masseter muscles and cause bilateral hypertrophy.
• Chewing on one side: Frequently eating on one side can lead to differences in tooth size between the left and right sides.

The self-assessment steps are as follows:

1. Clench your teeth: Stand in front of a mirror and clench your jaw tightly, then check to see if there is noticeable bulging on both sides of your jawline.
2. Check with your finger: While clenching your teeth, feel the area above the angle of your jaw; if you feel a distinct lump, it may indicate hypertrophy of the masseter muscle.
3. Relax and feel it again: If it feels soft after you relax and your cheeks are generally on the fuller side, the proportion of fat may be higher.

For some people, a large face isn’t actually caused by the masseter muscle. If you receive injections without first addressing this, the results will be limited, and you may end up wasting your money. It’s recommended that you consult a doctor first to determine whether this treatment is right for you.

In addition, masseter muscle injections for facial slimming are considered off-label use, but they are quite common in Asia,A review of 36 articles published in the *Journal of Cosmetic Dermatology* in 2018It is noted that Botox injections are a commonly used treatment for the masseter muscle; they are effective and safe, and any discomfort following the injection usually subsides gradually.

How Botox Works to Slim the Face: Why Injecting Botox into the Masseter Muscle Makes It Smaller

Botox acts on the neuromuscular junction, blocking the transmission of acetylcholine signals between nerves and muscles, thereby preventing muscle contraction. When botulinum toxin is injected into the masseter muscle, the muscle remains relaxed. This triggers the body’s disuse atrophy mechanism—just as muscles become thinner when not exercised—and because the masseter muscle is used less, its volume gradually decreases.

Once the mass of the masseter muscles protruding on both sides of the lower jaw is reduced, the previously square and broad jawline (commonly known as a “square face” or “masseter hypertrophy”) becomes smoother and softer, creating a visual effect of a “slimmer face.”

A systematic review incorporating 28 studiesThe study noted that 3 months after injection, the thickness of the masseter muscle decreased by an average of approximately 12% to 31%, depending on the number of injection sites. The review also noted that the effectiveness of Botox for facial slimming varies from person to person, and because there are significant differences in study methods and a high risk of bias, it is difficult to directly compare the merits of different injection techniques.

How Many Units of Botox Are Needed for a Slimmer Face? How Is the Dosage Calculated?

The dosage required for Botox to slim the face (by reducing masseter muscle hypertrophy) typically ranges from 30 U to 80 U (total for both sides). The specific dosage is not arbitrarily determined but is determined by the physician based on a comprehensive assessment of the masseter muscle’s development, facial structure, and the patient’s individual expectations.

Degree of Development of the Masseter Muscle	Estimated Total Dose for Both Sides (Using Botox as an Example)	Applicable to
Mild Hypertrophy	30 U – 40 U	When clenching the teeth, the masseter muscles on both sides bulge only slightly, and the overall contour remains fairly smooth.
Moderate hypertrophy	40 U – 60 U	Most common dosage; a noticeable lump when clenching the teeth; the cheeks are somewhat wide on both sides
Severe Hypertrophy	60 U – 80 U+	When clenching my teeth, I feel a very thick, hard lump, and I even experience severe teeth grinding.

(The actual dosage must be determined by a physician after assessing the thickness of the masseter muscle through palpation; the figures in this article are for reference only.)

In addition, recommended dosages for botulinum toxin injections vary across different sources:

Source	Dosage	Notes
Korean Journal of Dermatology	3 injections per side, 24–30 U	This is an older model; please take note before use.
Botox Phase 3 Clinical Trial (Exclusive Interview with Dermatology Times)	3 units per side, 8 U per unit, 24 U per side, for a total of 48 U	Brand Experiment Design
Randomized, Double-Blind, Dose-Randomized Trial (prabotulinumtoxinA)	24, 48, 72, and 96 U all significantly reduce masseter muscle thickness; 48–72 U is recommended, with a repeat injection after 12 weeks.	24 U may not be sufficient for correcting a square face

As mentioned earlier,Systematic ReviewIt was found that different injection patterns—such as at the 1 o'clock, 2 o'clock, 3 o'clock, and 6 o'clock positions—resulted in similar degrees of reduction at the 3-month mark; therefore, the authors concluded that, until stronger evidence becomes available, the number of injection sites should be kept to a minimum.

There are also doctors who*The Aesthetic Guide*Based on his experience, he believes that the degree of masseter muscle hypertrophy varies from person to person, so injections should be administered only where hypertrophy is palpable, rather than following a fixed injection pattern. Although this is the expert’s personal opinion, it supports the recommendation that a physician should perform a physical examination first.

Muscle Thickness

The thicker the masseter muscle, the higher the dose required. For people with thinner muscles, an excessively high dose can more easily lead to a feeling of weakness and unnatural indentations. This is why the doctor will ask you to clench your teeth and then palpate and mark the injection sites one by one.

Fat Percentage

Botox is effective only on muscles; it has no effect on fat. Therefore, the doctor will first gently pinch the skin to assess the thickness of the subcutaneous fat. If the primary cause of a large face is thick subcutaneous fat, Botox injections will have limited effectiveness. Blindly increasing the Botox dosage may actually cause facial tissues to lose support due to muscle atrophy, resulting in sunken areas or sagging.

Brand Selection

The definitions of active units (Unit) and the range of diffusion vary among different brands of botulinum toxin:

• U.S. Botox / South Korean Letybo / South Korean Nabota (Miracle Botox), etc.:
  • Using standard Speywood Units or Allergan Units as a reference, these dosage units are commonly used as a basis for estimating doses on the market (such as the 40–60 U mentioned above).
• Dysport (Lishutu) in the UK:
  • Because the units of measurement differ, 1 U of Botox is generally equivalent to 2.5 to 3 U of Dysport. If Dysport is used to treat both masseter muscles, the total dose required is approximately 100 to 150 U.
• Xeomin (Angel Botox) from Germany:
  • It contains no complex proteins and is less likely to trigger an antibody response; the dosage is comparable to that of Botox, with approximately 40 U to 60 U required for both sides.

How do I choose a Botox brand?

More important than the brand is that the product is legal.Statement from the Food and Drug AdministrationBotulinum toxin is a high-risk biologic drug that requires a drug license and must undergo batch-by-batch testing and sealing; the outer packaging of qualified products will bear a “Drug Inspection Certificate.” Three key points for identification:

• The outer packaging displays the Chinese license number and product name.
• The drug inspection certificate is securely affixed to the product's seal.
• The lot numbers, manufacturing dates, and expiration dates on the outer box and the inner bottle are the same.

The number of licenses varies over time; the Food and Drug Administration initially announced three licenses,A 2025 report indicated that seven permits have been approved to date.. We recommend checking the Food and Drug Administration’s Western Medicine Approval Database for the latest information.

Botox (Classic Botox)

• Manufacturer: Allergan (AbbVie), U.S.A.
• Features: Longest history on the market; extensive clinical data.
• Characteristics and Advantages: Stable molecular weight and precise diffusion range. After injection, the drug is unlikely to diffuse into non-target muscles, ensuring high safety and consistent duration of action.
• Indications: According toU.S. Prescribing Information, The FDA-approved indications are glabellar lines, crow’s feet, forehead lines, and the platysma band; the masseter muscle is currently considered an off-label use.
• Ideal for: First-time Botox users, those who prioritize precision (such as for fine areas like crow’s feet and forehead lines), or those seeking classic results.

Nabota (Rainbow Botox)

• Country of Origin: Developed by Daewoong Pharmaceutical in South Korea; the outer packaging features a rainbow anti-counterfeiting label, and it is commonly known as “Rainbow Botox.” It is also the first South Korean Botox brand to receive U.S. FDA approval.
• Features and Advantages: Utilizing patented high-purity extraction technology, it is characterized by rapid onset of action and consistent quality.
• Ideal for: People who want to see results quickly and are looking for a product that combines the value of a Korean brand with the safety assurance of U.S. FDA certification.

Dysport (Royal Botox)

• Manufactured by Ipsen in the United Kingdom.
• Characteristics and Advantages: It is generally considered to have a wider diffusion range, making it suitable for muscle relaxation over large areas; when used on the masseter muscle, physicians pay special attention to the injection site and depth. Note that its unit of measurement (Speywood U) differs from that of Botox; approximately 2.5 to 3 U of Dysport is equivalent to 1 U of Botox.
• Recommended for: Large muscle groups (such as the shoulders, trapezius, and calves), relaxation of extensive masticatory muscles, or those who want to see results quickly within a few days.

Xeomin (Angel Botox)

• Manufactured by Merz in Germany.
• Features and Benefits: This product is a “pure botulinum toxin” formulated without any complex proteins. By removing excess impurity proteins, it significantly reduces the likelihood of the body developing “resistance (antibodies).”
• Ideal for: Those who require frequent, regular treatments; those who have tried other brands and found the results to be less effective; and those seeking the ultimate in natural relaxation.

Letybo Baotila

• Country of Origin: Hugel, South Korea.
• Features and Benefits:Approved by the U.S. FDA on February 29, 2024, indicated for moderate to severe glabellar lines in adults; specifically designed for the muscle structure of Asian individuals; affordable and consistent in quality.
• Ideal for: Young professionals, those on a tight budget, people looking for great value, or anyone who wants to maintain a slimmer face or reduce wrinkles through regular, minor treatments.

Brand Name	Origin	Range of Spread	Features and Benefits	1U Market Price Reference
Botox	United States of America	Precise	The original classic, with the most documentation and consistent results	Approximately 150–300 yuan per U
Xeomin Jing You Ming	Germany	Moderate	Does not contain complex proteins; does not readily trigger the production of antibodies	Starting at about 150 per U
Dysport Lizi	United Kingdom	Larger	Wide-ranging and fast-acting, suitable for large muscle groups	Starting at about 150 per U (unit calculation methods vary)
Nabota	Korea	Moderate	Approved by the U.S. FDA; takes effect quickly	Starting at about 120 per U
Letybo Baotila	Korea	Moderate	Great value for the price, designed to suit Asian body types	Starting at about 100 per U

(Note: The prices in the comparison table represent the typical price range in the Taiwanese market. The actual pricing method (whether based on treatment area packages or the number of units) and the final amount are subject to the on-site assessment and quotation provided by the physician at each medical clinic.)

Extended Reading:Botox vs. Nabota: The Right Way to Get Botox for Every Part of Your Face

What are the side effects of Botox injections into the masseter muscle?

Most side effects of Botox injections into the masseter muscle are mild and temporary. As long as you choose an experienced, qualified physician and genuine, manufacturer-approved medication, most conditions will resolve within a few weeks to a few months as the effects of the medication wear off. Common side effects and aftereffects include:

Facial Asymmetry

If there is a difference in the strength of the masseter muscles on both sides, the dosage is improperly distributed, or the solution spreads unevenly, this may result in uneven corners of the mouth or asymmetry between the left and right sides of the face when smiling. This can be corrected through minor adjustments and additional injections administered by a physician.

Sagging

When the masseter muscles are significantly relaxed, the muscle tone that normally supports the tissues of the middle and lower face weakens. If the skin is already somewhat loose or the person is older, the middle and lower face may show slight sagging, or jowls may become more noticeable.

Sunken Cheeks

Commonly known as “sunken face” or “sunken cheeks.” When Botox spreads to the area above the masseter muscle (below the cheekbones), causing excessive atrophy of the muscles in that region, or in individuals with naturally high cheekbones or low cheek fat, the cheeks may appear sunken and unhealthy after treatment.

Frog Gills

Within 1 to 2 weeks after a Botox injection, abnormal bulging (similar to a frog’s vocal sac) may appear in the local muscles when you clench your teeth. This occurs because part of the masseter muscle has been relaxed, while the remaining muscle—not yet affected by the medication—contracts excessively to compensate. You may ask your doctor to evaluate whether a small additional dose of Botox is needed to relax the remaining muscle.

Unable to bite into hard objects

Once the Botox takes effect, the tension in the masseter muscles decreases, during the first 1 to 2 weeks, you may experience mild soreness and weakness in your cheeks when eating chewy or hard foods (such as guava, beef jerky, or shredded squid). This is a normal reaction to the treatment, and you will gradually adapt over time. An early study Small-scale studyIt was noted that, out of 20 participants, 2 experienced weakness and soreness in both cheeks after chewing vigorously, and 1 experienced mild, temporary weakness in the cheeks.

Reports from abroad indicate that botulinum toxin may spread from the injection site, leading to excessive muscle weakness, difficulty swallowing, and even life-threatening aspiration pneumonia; therefore,As a result, the U.S. FDA has required drug manufacturers to strengthen their warning labels.Please be aware that adverse reactions of this nature may occur. If you experience difficulty swallowing, shortness of breath, or generalized weakness after surgery, seek medical attention immediately.

Contraindications and Precautions for Botox Facial Slimming

Who Shouldn't Get Botox?

• Patients with neuromuscular disorders: Patients with neuromuscular junction disorders, such as myasthenia gravis, should not undergo botulinum toxin treatment.
• Minors: In accordance withAnnouncement from the Ministry of Health and Welfare, Individuals under the age of 18 may not undergo cosmetic surgery that is not medically necessary; those under the age of 20 must have a consent form signed by their legal guardian.
• If the intended injection site is inflamed or infected: Wait until the skin has healed before reassessing.
• Other situations that require prior consultation with a doctor: Pregnancy, breastfeeding, allergy to botulinum toxin, infection at the injection site, or if you are taking certain medications—please refer to the package insert and consult your doctor for guidance.
• Allergy to botulinum toxin or any of its components.

Precautions Before Vaccination

• Discontinuation of Anticoagulants and Dietary Supplements: It is recommended to stop taking aspirin, fish oil, ginkgo, vitamin E, and similar supplements one week before surgery to reduce the likelihood of bruising at the injection site.
• Provide a Complete Medical History: Proactively inform your doctor of your past medical history, any medications you are currently taking, and any recent cosmetic procedures you have undergone.
• Accurately assess your face shape: If your face appears large primarily due to “fat accumulation” or a “wide bone structure,” the effects of Botox will be quite limited.
• Ask for clear details: including the brand being used, the expected dosage, the total cost, possible side effects, and how to handle them.

Post-Vaccination Precautions

• Avoid lying flat or sleeping on your stomach for the first 4 hours: Remain in an upright position, and avoid massaging or rubbing the injection site to prevent the medication from spreading to non-target muscles.
• Avoid strenuous exercise and alcohol for 24 hours.
• Avoid environments with high heat for one week: Avoid saunas, hot springs, and steam rooms, and do not wash your face with water that is too hot.
• Reduce the habit of chewing hard objects: After surgery, avoid chewing hard items such as gum, nuts, and pearls to help prolong the slimming effect on your face.

In 2025, the Ministry of Health and Welfare reported a caseA woman purchased Botox online and had the seller come to her home to administer the injection. Three days later, she developed difficulty swallowing, impaired saliva secretion, drooping eyelids, and muscle weakness, requiring intubation and a ventilator. Although Botox injections are convenient and minimally invasive, they carry certain risks. Therefore, it is essential to choose a legally licensed medical facility and not take risks just to save money.

Case Study: Botox for a Slimmer Face at Arixin Clinic

1. Customer Identification and Referral

An engineer who experiences high work stress and often needs to focus on a screen for long periods of time had, without realizing it, developed the habits of clenching his teeth and grinding them while sleeping. Over time, the masseter muscles on both sides of his jaw became increasingly developed, making his face appear squarer and wider—especially his cheekbones, which were particularly noticeable when viewed from the front. and often felt that his facial contours weren’t sharp enough when taking photos or participating in video conferences. Since he frequently came across posts about Botox for facial slimming while scrolling through his phone, and because he wanted to improve his facial contours to look better on camera, he decided to schedule a consultation at Arixin Clinic.

2. Doctor's Diagnosis

After performing a physical examination, the doctor determined that the patient’s masseter muscles on both sides were indeed hypertrophied, resulting in a “square face” caused by overuse of the masseter muscles. The doctor recommended using Botox to slim the face by reducing the masseter muscles.

The doctor explained that Botox is the first botulinum toxin brand to be marketed globally. It is approved by the U.S. FDA and delivers stable, precise results. After injection, it gradually relaxes and reduces the size of overdeveloped masseter muscles, causing facial contours to gradually soften, while also helping to alleviate teeth grinding.

The doctor assesses the appropriate injection dose based on the thickness and size of the patient’s masseter muscles, ensuring a natural reduction in facial volume without affecting normal chewing function.

3. Treatment Process

On the day of the treatment, the doctor first asks the patient to clench their teeth tightly, then palpates the area to determine the extent and thickness of the masseter muscles on both sides. After marking the injection sites, the procedure begins. An extremely fine needle is used, and the procedure causes only a slight prickling sensation. The entire session takes about 10 to 15 minutes and requires no additional recovery time; you can return to work immediately afterward.

The doctor also advised me to avoid facial massage, bending my head forward, sleeping in bed, and strenuous exercise for 4 hours after the treatment. If I experience any discomfort, I should return for a follow-up visit as soon as possible.

4. Results

About 4 to 6 weeks after treatment, the patient gradually noticed that the masseter muscles on both sides were relaxing and shrinking, and her facial contours became smoother and more defined than before. This is evident in both front-view and side-view photos, which show that her facial contours are smoother and more defined than before, and her jawline has become softer. Now, whether taking selfies or participating in video conferences, my facial contours look more flattering from every angle.

Frequently Asked Questions About Botox for a Slimmer Face

Recommended Aesthetic Clinics in Taichung for Botox Facial Slimming | Arixin Clinic

When it comes to facial contouring, the most important factor is that the results “suit you,” not that they are “the smaller, the better.” At Arixin Clinic, the doctor will first perform a physical examination to assess the thickness of your masseter muscles, any asymmetry between the left and right sides, and your fat distribution. They will then explain which brand and dosage are appropriate for you and ensure you fully understand the possible side effects. Only after you’ve had sufficient time to consider your options will you decide whether to proceed with the treatment.

• Professional Palpation Assessment: A qualified physician personally palpates the masseter muscle to assess its thickness and elasticity, accurately calculating the dosage to avoid over- or under-treatment.
• Guaranteed Genuine Products: We offer a variety of botulinum toxin brands approved by the Ministry of Health and Welfare (such asBotox in the U.S.(such as Germany’s Xeomin and South Korea’s Letybo), opened on-site for your peace of mind and assurance.
• Customized Fine-Tuning: We create a natural, well-defined jawline tailored to individual needs, such as teeth grinding, facial asymmetry, or masseter muscle hypertrophy.

The actual dosage and choice of brand will be determined after a physician assesses the thickness of your masseter muscle through an in-person physical examination. Schedule an appointment today for a one-on-one consultation with a physician and take the first step toward a refined, sleek facial contour!