HCG Diet: Protocol, Results, and Safety Guide

The HCG diet combines daily HCG hormone injections with an extremely restrictive 500-calorie daily diet, promising rapid weight loss of 1-3 pounds per day. This comprehensive guide explores the Simeons protocol, scientific evidence for HCG effectiveness, the diet's three phases, significant health risks associated with very-low-calorie approaches, and how modern GLP-1 medications like Ozempic have substantially replaced the HCG diet as the preferred weight loss approach.

What Is the HCG Diet and How Did It Originate?

The HCG diet combines human chorionic gonadotropin (HCG) injections with an extreme calorie restriction diet, based on a protocol developed in the 1950s by British physician Dr. Albert Simeons.

HCG is a hormone naturally produced during pregnancy, detected by pregnancy tests, and used medically to treat certain infertility conditions. Dr. Simeons theorized that HCG might mobilize abnormal fat stores and preserve muscle mass during severe calorie restriction, enabling rapid weight loss without lean tissue loss. He published his protocol in 1954 and the HCG diet has maintained a dedicated following for over 70 years despite limited scientific support.

The diet became popular particularly among celebrities and fitness enthusiasts seeking rapid weight loss. It achieved peak cultural relevance in the 1970s-1980s and has experienced periodic resurgences. The extreme nature of the regimen (daily injections, 500-calorie diet, very rigid food rules) both attracts people willing to undergo extreme measures for rapid results and repels those seeking practical, sustainable approaches.

The appeal is straightforward: the diet produces substantial, rapid weight loss. Patients report losing 1-3 pounds daily, with many losing 40-60 pounds over the typical 23-43 day treatment cycle. This is extraordinarily fast compared to typical weight loss programs. The speed creates psychological reinforcement and visible results. The extreme structure also reduces decision-making during the diet phase, potentially improving adherence compared to less-structured approaches.

The decline of the HCG diet in recent years correlates with the rise of GLP-1 receptor agonists (semaglutide, tirzepatide, etc.), which achieve similar weight loss with substantially less difficulty, more scientific support, and better safety profiles. For many people, the choice between the HCG diet and GLP-1 medications is now obvious; GLP-1s offer superior outcomes with less hardship.

The Simeons Protocol: The Three Phases Explained

The classic HCG diet protocol divides into distinct phases, each with specific calorie targets, HCG dosing, and food guidelines. Understanding the phases clarifies the regimen's structure and rationale.

Phase 1 is the loading phase lasting 2-3 days. Patients begin daily HCG injections while eating unrestricted, high-fat, high-calorie foods. The rationale is building fat reserves for the upcoming severe calorie deficit. Patients typically consume 3,000-4,000+ calories daily, eating foods like bacon, eggs, avocado, cheese, and rich desserts. The contrast between loading phase eating and Phase 2 restriction is extreme. Some patients find this phase enjoyable (eating without restriction); others find the transition psychologically jarring.

Phase 2 is the primary weight loss phase lasting 23-43 days (or longer for some protocols). This phase defines the HCG diet experience. Patients continue daily HCG injections and restrict daily calories to exactly 500 (sometimes 600-800 in modified versions). The diet consists of very specific foods in exact portions: 2 meals daily (breakfast and lunch, skipping dinner), each containing 3.5 ounces of protein (chicken, fish, beef), one vegetable from an approved list, one bread item (usually a single piece of toast), and one fruit from an approved list. Drinks are limited to water, black coffee, or tea. No oil, butter, or condiments beyond salt, pepper, and spices.

The 500-calorie target is below minimum recommended daily intake for any adult (1,200 for women, 1,500 for men). This extreme restriction causes rapid weight loss. Studies show average weight loss is 1-2 pounds daily, sometimes exceeding 3 pounds daily. Over 43 days, patients lose 50-80+ pounds. The speed is the appeal but also reflects the extreme nature of the calorie deficit. Most of this rapid weight loss includes fat loss (the goal) plus water loss and muscle loss (the downsides).

Phase 3 is stabilization lasting 3 weeks after stopping HCG injections. Calories gradually increase from 500 to 1,500-1,800 while avoiding starches and sugars. The rationale is allowing the body to stabilize at the new lower weight without triggering rapid weight regain. Patients continue following specific foods and portions but with increased quantities. Weight typically remains stable during this phase or increases slightly (1-5 pounds) from water and muscle glycogen restoration, not fat regain.

Phase 4 is long-term maintenance, theoretically lasting indefinitely. Patients resume normal eating patterns while maintaining weight loss. The theory is that the previous phases have permanently recalibrated weight set-point. In practice, many people struggle with Phase 4, gradually returning to pre-diet eating patterns and regaining weight. This phase has no specific HCG diet structure; it's essentially conventional weight maintenance.

The Science Behind HCG: Does the Hormone Actually Help Weight Loss?

Despite decades of clinical use and patient enthusiasm, scientific evidence for HCG's role in weight loss is surprisingly weak, with multiple well-designed studies finding no advantage over placebo.

The theoretical mechanism is that HCG mobilizes abnormal (lipid-localized) fat for energy during calorie restriction, allowing the body to access stored energy without hunger, while preserving muscle mass. The theory is biologically plausible but unproven. HCG receptors don't exist on human fat cells, undermining the proposed mechanism.

Clinical research systematically examining HCG's efficacy has consistently found similar results across multiple studies. When researchers compare HCG injections to placebo injections while maintaining identical 500-calorie diets, weight loss is nearly identical between groups. A 1995 meta-analysis reviewing 16 controlled HCG studies found HCG provided no benefit over placebo for weight loss when calories were controlled. Subsequent studies have replicated these findings.

What about muscle preservation? HCG was theorized to preserve lean mass during VLCD. Some studies suggest marginal benefits (perhaps preserving slightly more muscle mass with HCG vs. placebo), but the difference is modest at best. Even if true, muscle preservation during a 500-calorie diet is likely limited regardless; extreme calorie restriction causes muscle loss even with HCG.

One possibility is that HCG might improve appetite suppression during extreme calorie restriction, making the 500-calorie diet more tolerable. However, research directly examining appetite under HCG is limited. Subjective reports suggest HCG may reduce hunger somewhat, but placebo effects (expecting hunger reduction) likely contribute substantially.

A major consideration is publication bias. Studies finding HCG ineffective are published less frequently than positive studies. Additionally, HCG diet clinics and practitioners conducting research have obvious financial incentives to report positive results. Many studies lack rigorous control groups or blinding. When high-quality controlled research is reviewed, HCG advantage largely disappears.

The most parsimonious explanation is that weight loss on the HCG diet results from the 500-calorie restriction, not HCG itself. The hormone may provide modest psychological benefit or marginal physiological advantage, but these don't account for the dramatic weight loss achieved. Extreme calorie restriction is extraordinarily effective for weight loss; HCG appears unnecessary to the equation.

HCG Diet Results: What Weight Loss Can Actually Be Expected?

HCG diet results in rapid, substantial weight loss, making it one of the most effective short-term weight loss approaches. Understanding realistic expectations helps evaluate whether the diet is appropriate for your goals.

Daily weight loss during Phase 2 averages 1-2 pounds per day, with some individuals losing up to 3 pounds daily. This rate far exceeds typical weight loss programs (typically 1-2 pounds weekly). Over a standard 43-day protocol, patients lose approximately 40-80 pounds depending on starting weight and individual variation. Higher starting weights tend to produce faster initial weight loss.

Total weight loss includes fat loss (the desired outcome) plus water loss (temporary) plus muscle loss (undesirable but inevitable with VLCD). Estimates suggest that of the 2-3 pounds lost daily, approximately 1-1.5 pounds is fat, 0.5-1 pound is water, and 0.5 pounds is muscle. The percentage of lean tissue loss increases the longer the diet continues.

Visible results appear rapidly. Within 1-2 weeks, significant weight loss becomes noticeable in appearance. Clothes fit differently, the scale drops noticeably, and visual transformation occurs. This rapid visible change provides psychological reinforcement and motivation continuation. The visible results are one reason people maintain extreme diet adherence despite hunger and difficulty.

Results vary substantially between individuals. Some people lose at predicted rates; others lose more slowly. Age, metabolism, starting weight, exercise, and individual physiology affect rate. Women often lose slightly more slowly than men at comparable calorie restriction. The HCG protocol accepts this variation; significant weight loss occurs across the population despite individual differences.

Metabolic adaptation becomes important during Phase 2. As weight loss progresses, the body adapts to reduced calories, decreasing energy expenditure. This causes weight loss to slow over time. Early weeks might show 3 pounds daily loss; later weeks might show 1 pound daily. This is normal physiology and doesn't indicate diet failure, but it affects total expected weight loss.

Phase 3 stabilization typically shows minimal additional weight loss (0-3 pounds) or slight weight gain (3-5 pounds). The weight gain is usually water and glycogen restoration, not fat regain. Weight should stabilize around the Phase 2 endpoint. If significant weight is regained during Phase 3, this may indicate inadequate Protocol adherence.

The critical question is long-term maintenance. Post-diet weight regain is substantial for most people. Without addressing underlying factors driving weight gain (eating behaviors, hunger biology, lifestyle), approximately 70-80% of people regain significant weight within 1-2 years. The rapid weight loss is impressive short-term; sustainable weight maintenance is the actual challenge the HCG diet doesn't adequately address.

FDA Warnings and the Regulatory Status of HCG Products

The FDA has issued explicit warnings that OTC HCG products are unapproved drugs, and has taken enforcement action against vendors making unsubstantiated weight loss claims.

HCG as a prescription medication is legitimate. The FDA approved HCG injections (brands like Pregnyl and Novarel) for treating certain infertility conditions. These are FDA-approved pharmaceuticals produced under GMP standards with verified purity and potency. Prescription HCG for medical purposes is legal and regulated.

The problem the FDA identified is OTC HCG products. Starting around 2000, various companies began selling HCG products for weight loss without FDA approval. These products came in multiple forms: injectable, oral drops, pellets, supplements. The vendors marketed them explicitly for weight loss, often without mentioning the Simeons protocol specifically but clearly targeting the weight loss market.

In 2011, the FDA warned that OTC HCG products are unapproved new drugs and declared them illegal to market without approval. The agency specifically stated that marketing claims (that HCG enables safe weight loss on VLCD without muscle loss, increases metabolism, redistributes fat) lack scientific support. The FDA stated these claims are false, unsubstantiated, and misleading.

The distinction is important: the FDA didn't say HCG is dangerous, but rather that OTC products are unapproved and marketing claims are unsubstantiated. The agency has pursued enforcement actions against particularly blatant violators, issuing warning letters to companies selling HCG for weight loss. Some companies have been forced to remove products or refrain from weight loss marketing.

Despite FDA warnings, OTC HCG products remain widely available online. Many vendors continue marketing HCG drops and supplements for weight loss, in clear violation of FDA guidance. The agency's enforcement resources are limited and enforcement actions tend to target the most egregious cases. Many OTC products remain available in a gray regulatory area.

Prescription HCG from a licensed physician avoids regulatory issues. A doctor can prescribe HCG for patients interested in the diet; the prescription is then filled by a pharmacy. This approach complies with regulations because HCG is being prescribed medically, not sold as an OTC weight loss product. Many HCG diet clinics and practitioners operate this way, having doctors supervise the diet and prescribe HCG.

Very-Low-Calorie Diet Risks: Health Concerns with Extreme Restriction

The 500-calorie daily intake is far below recommended minimums and carries significant health risks, particularly with extended duration. Understanding these risks is essential before attempting the HCG diet.

Muscle loss is inevitable and substantial. While Dr. Simeons claimed HCG preserves muscle, the extreme calorie deficit ensures lean tissue loss occurs. Estimates suggest 25-30% of weight loss is muscle or other lean tissue, not fat. For someone losing 50 pounds, approximately 12-15 pounds is muscle loss. The 500-calorie diet simply doesn't provide enough protein and calories to maintain muscle. Muscle loss reduces metabolic rate (muscle burns more calories at rest than fat), making future weight maintenance harder. Strength decreases during the diet and may not fully recover post-diet.

Nutritional deficiencies are common due to extremely limited food intake. Even the allowed foods don't provide adequate vitamins and minerals for health. The diet typically lacks sufficient iron, calcium, vitamin D, vitamin B12, and other micronutrients. Extended VLCD causes deficiency risks particularly for vitamin B1, folate, and other nutrients. Fatigue, weakness, hair loss, and immune dysfunction can result. Proper supplementation during the diet can mitigate some risk but doesn't eliminate the inherent nutritional inadequacy of 500 calories daily.

Gallstones form in 10-25% of people undergoing rapid weight loss, particularly extreme rapid loss. The mechanism involves bile stasis from decreased fat intake and dietary changes. Gallstones may remain silent or cause severe pain and inflammation. Some require surgical removal. The younger and leaner the person, the lower the gallstone risk; obese women have highest risk. The 1-3 pound daily loss is fast enough to substantially increase gallstone risk.

Metabolic adaptation (adaptive thermogenesis) occurs with prolonged VLCD. The body, sensing energy scarcity, decreases energy expenditure below what the reduced calories predict. Basal metabolic rate can decrease 20-30% during extended VLCD. This makes future weight maintenance harder because the lower metabolism persists post-diet. Regaining weight is easier and maintaining weight loss is harder after metabolic adaptation from VLCD.

Hormonal disruption occurs with extreme calorie restriction. Thyroid hormone production decreases, leptin (hunger hormone) drops, cortisol (stress hormone) increases. Women commonly experience menstrual irregularities or amenorrhea during VLCD. Fertility may be affected. Mood changes (depression, anxiety) are common from calorie restriction and hormonal changes. Sexual dysfunction and libido changes occur. These hormonal disruptions persist somewhat post-diet even as calories increase.

Electrolyte imbalances are possible, particularly potassium, sodium, and magnesium. Imbalances can cause muscle cramps, weakness, and potentially dangerous cardiac arrhythmias. Proper monitoring and supplementation can prevent severe imbalances, but the restrictive diet increases risk.

Fatigue and reduced energy are near-universal during Phase 2. The 500-calorie intake is insufficient for normal activity; patients report feeling tired, experiencing brain fog, struggling with concentration. Exercise is essentially impossible during the diet; even walking is difficult for some. This reduced activity further contributes to muscle loss. For people needing to work or maintain normal responsibilities, the energy depletion is particularly problematic.

Cardiovascular stress is a concern, particularly for people with existing heart conditions. Extreme weight loss stresses the cardiovascular system. ECG abnormalities have been noted in some VLCD patients. People with heart disease should avoid VLCD without medical supervision.

Medical Supervision and Safety Considerations

The HCG diet's risks necessitate medical supervision, though unfortunately much commercial HCG diet marketing bypasses appropriate medical oversight.

Appropriate medical supervision should include baseline health assessment confirming the patient is healthy enough for extreme calorie restriction. Cardiac risk should be assessed. Electrolyte screening and baseline metabolic panel should be obtained. The physician should monitor progress, weight loss rate, side effects, and tolerance throughout the diet. Regular follow-up (ideally weekly or bi-weekly) should assess wellbeing, medication interactions, and complications.

Many commercial HCG diet providers claim medical supervision but provide minimal actual physician involvement. Telemedicine visits where a doctor prescribes HCG but has minimal ongoing patient contact don't constitute adequate supervision. Ideal supervision includes direct physician-patient contact, appropriate pre-diet screening, and close monitoring throughout.

Certain people should avoid the HCG diet entirely: pregnant women (HCG could theoretically affect pregnancy), people with history of blood clots, people with active cancer, people with significant heart disease, people taking certain medications with interactions, people with kidney disease or hepatic disease, people with a history of eating disorders, and people with psychiatric conditions like depression or bipolar disorder. The extreme nature of the diet is contraindicated for many conditions.

Pre-diet screening should include complete metabolic panel, lipid panel, thyroid function, baseline weight and measurements, and cardiac risk assessment. Blood pressure monitoring is important. For people on medications, drug interactions and medication adjustments should be considered. Some drugs are affected by extreme calorie restriction; dosing may require adjustment.

HCG Diet vs. Modern GLP-1 Medications: Why GLP-1s Are Preferred

The emergence of GLP-1 receptor agonists (semaglutide, tirzepatide) has fundamentally altered weight loss treatment paradigms, making the HCG diet largely obsolete for most people.

Weight loss efficacy is comparable. The HCG diet achieves 40-80 pounds over 43 days (extreme speed). GLP-1 medications achieve 15-22% body weight reduction over several months (moderate speed). For a 200-pound person, HCG achieves 30-40 pounds in 6 weeks; GLP-1s achieve 30-44 pounds over 6 months. The total weight loss is similar, but the speed differs. GLP-1s are slower but sustainable.

The hunger experience is fundamentally different. On the HCG diet, patients consume 500 calories while experiencing significant hunger; this is pure white-knuckle willpower. On GLP-1s, patients feel naturally full on 1,500-1,800 calories; hunger is reduced or absent. The psychological and physical experience is vastly different. Most people would vastly prefer GLP-1's mechanism to HCG's.

Safety profiles favor GLP-1s. GLP-1 medications have extensive clinical trial data, FDA approval, and long-term safety profiles. Side effects (nausea, vomiting, diarrhea, constipation) are generally mild and improve with time. HCG diet risks (muscle loss, gallstones, metabolic disruption, nutritional deficiency, hormonal dysfunction) are more substantial, particularly with extended duration.

Long-term weight maintenance differs substantially. GLP-1s provide ongoing appetite suppression, helping maintain weight loss. Stopping GLP-1s typically leads to weight regain, but resuming medication re-suppresses appetite. Continuing GLP-1s long-term enables sustained weight loss. The HCG diet achieves weight loss then relies on behavioral maintenance; most regain weight. GLP-1s provide biological support for maintenance; this is a major advantage.

Scientific evidence strongly supports GLP-1s. Multiple large randomized controlled trials show efficacy and safety. The mechanism is understood and validated. HCG's mechanism remains unproven; the hormone appears unnecessary for weight loss. GLP-1s are built on stronger evidence.

Additional GLP-1 benefits beyond weight loss include improved blood sugar control, reduced cardiovascular disease risk, improved metabolic markers, and reduced appetite for certain foods (particularly highly palatable foods). The HCG diet produces weight loss but doesn't provide these additional benefits.

Cost differs. GLP-1s cost $1,200-1,500 monthly uninsured (reduced with insurance or assistance programs). HCG diet costs vary ($800-2,000+ for clinic programs) but are generally lower. For uninsured patients, cost might drive HCG diet selection, though manufacturer assistance programs for GLP-1s often reduce costs substantially.

Long-Term Weight Maintenance After HCG Diet

Maintaining weight loss after the HCG diet is challenging and represents the diet's major long-term limitation. Many people regain weight despite achieving impressive short-term results.

Phase 3 stabilization attempts to set a new weight set-point through gradual calorie increases while maintaining dietary structure. The theory is that hypothalamic set-point (the weight your body tries to maintain) resets downward from HCG treatment and Phase 2 restriction. Whether this actually occurs or is just theory is debated. Regardless, when Phase 4 unrestricted eating begins, many people struggle.

The HCG diet doesn't address underlying drivers of obesity. Eating behaviors, food relationships, emotional eating patterns, stress response, activity levels, and environmental factors remain unchanged post-diet. Without addressing these fundamentals, people often return to pre-diet eating patterns and regain weight. The diet temporarily forces compliance through extreme structure; ending the structure removes the forcing function.

Metabolic adaptation from the extreme calorie restriction persists. The metabolic rate remains lower post-diet even as calories increase. This makes maintaining weight loss harder; fewer calories are burned at rest than before the diet. This metabolic disadvantage can persist months or years.

Hunger increases post-diet. During Phase 2 extreme restriction, hunger is suppressed (either from HCG, the diet structure, or adaptation to starvation). As calories increase in Phase 3 and 4, hunger returns. Without mechanisms to continue suppressing appetite (like GLP-1s provide), hunger drives increased eating and weight regain.

Long-term success requires sustained behavioral changes. People maintaining HCG weight loss long-term typically continue following modified versions of the diet (higher calories but maintaining dietary restrictions), exercise regularly, monitor weight closely, and intervene with temporary re-restriction if weight increases. This requires permanent vigilance.

Approximately 70-80% of people regain substantial weight within 1-2 years post-HCG diet. This is consistent with other VLCD approaches. The rapid weight loss is impressive; sustained weight loss is uncommon. This is a major reason why GLP-1s are preferred—they provide biological support for maintenance, not just temporary weight loss.

Comparing HCG Diet to Other Weight Loss Approaches

Understanding how the HCG diet compares to other weight loss methods helps contextualize its role in the modern weight loss landscape.

vs. Moderate Calorie Deficit (500-1,000 daily): The HCG diet's 500-calorie intake produces much faster weight loss than a 1,000-1,500 calorie moderate diet (1-2 pounds weekly). However, moderate calorie restriction has better sustainability, fewer health risks, more manageable hunger, and better long-term adherence. Most weight loss medicine recommends moderate restriction over extreme VLCD.

vs. Structured Weight Loss Programs (Weight Watchers, Nutrisystem): These programs provide moderate calorie restriction (1,200-1,500 daily) with behavioral support. Weight loss is slower than HCG (1-2 pounds weekly vs. 1-3 daily) but more sustainable. Adherence is better; side effects are fewer. Long-term weight loss rates are similar to HCG despite slower initial loss. The structure and support can benefit adherence.

vs. Exercise-Based Approaches: Regular exercise combined with modest dietary changes can produce 5-10% body weight loss. This is less than HCG or GLP-1s alone, but improves metabolic health, builds muscle, and is sustainable. As an adjunct to medication or dietary approaches, exercise is valuable. As the sole approach for obesity, it's usually insufficient.

vs. Behavioral Therapy: Cognitive behavioral therapy and coaching focusing on eating behaviors, stress management, and lifestyle changes can produce 5-10% weight loss. It's slower than HCG but teaches skills with long-term applicability. Combining behavioral therapy with other approaches (medication, dietary change, exercise) is synergistic.

vs. Bariatric Surgery: Gastric bypass, sleeve gastrectomy, and duodenal switch achieve 40-70% weight loss, more than any medical approach. However, surgery carries risks (1-2% mortality), requires lifelong dietary modifications, and isn't reversible. It's appropriate for severe obesity or when other approaches have failed. HCG diet is far less invasive, making it attractive to people unwilling to pursue surgery.

vs. GLP-1 Medications: As discussed extensively, GLP-1s are now preferred for most people due to better efficacy, safety, and long-term maintenance support. HCG diet is largely obsolete compared to GLP-1s.