At a glance
Effects
- Rapid visual muscle enlargement: Intramuscular oil creates the appearance of a larger muscle almost immediately after injection — effects can be visible within days [2][3].
- Cosmetic symmetry / 'fluffing': Some competitive bodybuilders use it to pad a visually lagging muscle group so it appears more proportionate on stage — known in bodybuilding circles as 'fluffing' [7].
- No strength increase: Because the volume is purely physical filler, no improvement in muscular strength or athletic performance is produced [2][4].
- No hormonal effect: Synthol has no androgenic or anabolic hormonal activity; it does not interact with androgen receptors or alter testosterone levels [1][2].
Site Enhancement Oil (SEO) — not a drug, steroid, or approved injectable filler
85% MCT oil, 7.5% lidocaine, 7.5% benzyl alcohol
Deep intramuscular injection only
No FDA approval for injectable use; sold legally as 'posing/topical oil' only
Immediate to days; damage can be permanent and irreversible
About Synthol
Every point here is drawn from public medical and harm-reduction sources. A bracketed number after a claim — like [1]— is a reference: tap it to open the exact source it's based on (numbered list at the bottom). It is not a rating or score. Educational information, not medical advice.
Product specifics
- Est. delivery
- 3–7 business days · EU tracked
Product details as stated by the vendor (claims, not independently verified). Delivery is our standard EU estimate.
What it is
Synthol is a site enhancement oil (SEO) — not a steroid or drug in the pharmacological sense — composed of approximately 85% medium-chain triglyceride (MCT) oil, 7.5% lidocaine, and 7.5% benzyl alcohol, injected intramuscularly by some bodybuilders to artificially increase the visual size of a target muscle [1][2]. It has no approved medical use as an injectable filler and provides no genuine strength or anabolic benefit [3][4].
How it works
When injected deep into a muscle belly, the oil physically displaces and expands the tissue between muscle fibres, acting like a foreign, semi-permanent volumising implant rather than stimulating any cellular growth [1][2]. The lidocaine component numbs the injection site during administration [2]. Over time, the body encapsulates the oil with fibrous scar tissue; the oil does not metabolise quickly, meaning volume changes can persist for years and damage can become irreversible [5][6].
Risks & side effects
Most important: If the needle inadvertently enters a blood vessel, oil can travel to the lungs and cause a potentially fatal pulmonary oil embolism [1][6]. Beyond this acute danger, repeated injections inevitably cause progressive muscle fibrosis — painful, potentially irreversible scarring that can destroy the target muscle and require surgical excision [5][8].
Common
Serious
- Chronic muscle fibrosis with painful nodules — may require open surgical excision [8][5]
- Abscess formation and recurrent bacterial infection [5][3]
- Nerve damage from improper injection technique [6][3]
- Oil-filled cysts within the muscle (MRI-visible fatty lesions) [8]
- Ulceration and chronic wounds at injection sites [6][10]
Rare
- Pulmonary oil embolism — potentially fatal blockage of the pulmonary artery [1][6]
- Myocardial infarction (heart attack) secondary to oil embolisation [6]
- Cerebrovascular accident (stroke) [6][3]
- Foreign body pulmonary granulomatosis from haematological migration of oil [11]
- Calcitriol-mediated hypercalcaemia leading to acute kidney injury and nephrocalcinosis [11][12]
Safety & harm reduction
- Anyone with cardiovascular disease, clotting disorders, or compromised pulmonary function — oil embolism risk is life-threatening [1][6]
- Anyone with active skin or muscle infection at the proposed injection site [5]
- Anyone with allergy to lidocaine or amide-type local anaesthetics [2]
- Anyone who is not prepared to accept the risk of permanent muscle fibrosis and potential surgical intervention [8][5]
- Unsupervised self-administration — improper injection technique dramatically increases risk of nerve damage, abscess, and vascular injection [3]
- Serum calcium levels — hypercalcaemia has been reported as a long-term complication of muscle granulomatosis [11][12]
- Renal function (creatinine/eGFR) — hypercalcaemia-related acute kidney injury is documented [11]
- Muscle MRI or ultrasound if pain, hardening, or deformity develops — to detect fibrosis or cystic lesions early [8]
- Signs of infection: local erythema, fever, fluctuant swelling — prompt antibiotic review and surgical assessment if abscess suspected [5]
- Concurrent anticoagulant or antiplatelet therapy may increase bleeding risk at injection sites [general injectable risk]
- Lidocaine component: additive toxicity possible if other local anaesthetics or sodium-channel-blocking agents are used simultaneously [2]
- No pharmacokinetic drug–drug interaction data exist — absence of data does not imply safety [4]
- No established safe protocol exists — there is NO medically approved dosing regimen for intramuscular Synthol use [4][3]
- Strict sterile technique is essential if use proceeds: single-use needles, aseptic prep of skin, never share equipment [3]
- Never inject into a vein or artery — aspirate before injecting; if blood appears in syringe, withdraw immediately [1]
- If fibrosis, persistent pain, or nodules develop, seek plastic or reconstructive surgical assessment promptly — delay worsens outcomes [5][8]
- The FDA has not analysed Synthol ingredients for injectable safety and has approved no SEO for large-scale body contouring [13]
Dosage context
No safe or medically approved dosing protocol exists for intramuscular Synthol use [4]. The FDA has not approved Synthol or any comparable site enhancement oil as an injectable [13]. Community-reported regimens (typically starting at 1 mL per site, escalating over weeks) circulate on bodybuilding forums but carry no clinical validation and are associated with the full spectrum of serious complications described above. This catalogue does not reproduce or endorse such regimens.
Sources
- 1.Biology Insights — Is Synthol a Steroid? Mechanism and Risks
- 2.Healthline — Synthol Injections: Uses, Dangers, and More (medically reviewed)
- 3.ResearchGate / PubMed — The Usage of Synthol in Bodybuilding (Pupka et al., 2009)
- 4.The Conversation — What is Synthol and why are bodybuilders injecting it?
- 5.PMC / NIH — Management of Synthol-induced Fibrosis (Nassar et al., 2024)
- 6.Indian Journal of Pharmaceutical Sciences — Cosmetic Abuse of Site Enhancement Oils: Insight Review
- 7.Wikipedia — Site Enhancement Oil
- 8.Springer / Journal of Medical Case Reports — Painful Muscle Fibrosis Following Synthol Injections (2012)
- 9.The Conversation — Synthol: Anaesthetic effects and pain
- 10.PMC / NIH — Intramuscular Synthol Injections Cause Hypercalcaemia (2024, case report)
- 11.PMC / NIH — Synthol Systemic Complications: Hypercalcaemia and Pulmonary Granulomatosis (Alimoradi et al., 2021)
- 12.ScienceDirect — Synthol Systemic Complications (Alimoradi et al., 2021)
- 13.LegitScript — Surge of Synthol Merchants: FDA Status and Risk
This information is provided for educational and harm-reduction purposes only. It is not medical advice. These substances can carry serious health risks; effects and safe use vary by individual. Consult a qualified healthcare professional before use. Legal status varies by country — it is your responsibility to know your local law. We do not encourage misuse.