If not, 6 mm or 8 mm needles will also work
10 Minutes 24-48 Hours 2-4 Weeks What Are Intramuscular Injections
With intramuscular injections of B12, any excess will result in high levels within your blood so you may experience side effects such as headache, dizziness, tiredness, or gastrointestinal issues including nausea, until your body has metabolised any excess through your kidneys enroute to excretion via urine

Brand: Royal Booster Product Name: Royal Booster Skin Whitening Injection Product Type: Intravenous (IV) Skin Brightening & Anti-Aging Injection Recommended Usage: 1 to 2 injections per month Maintenance Period: 3 to 4 months or more for best results Visible Results: As early as 3 days after first injection Skin Type: All Skin Types Skin Concerns: Hyperpigmentation, Dark Spots, Uneven Skin Tone, Dullness, Fine Lines, Wrinkles, Sagging Skin, Dark Underarms, Dark Inner Thighs, Freckles, Open Pores, Stretch Marks, Scars Free From: Parabens-Free | Sulphates-Free | Phthalates-Free | Toxic Chemicals-Free Origin: Premium Quality Formulation Administration: Must be administered by a licensed healthcare professional
However, this is controversial, and more evidence is needed
Perhaps this was confirmed in one of the clinical trials taking place in Australia, where nearly 300 obese individuals experienced weight loss