By Kelly Callis, FNP-C | Concierge Medical Clinic | Bradenton, FL

If you are on a GLP-1 medication like Semaglutide or Tirzepatide for weight loss, or on Testosterone Replacement Therapy (TRT), you are already making a powerful investment in your health. But there is something most providers forget to tell you — these therapies work even better when your body has the right nutritional foundation to support them.

GLP-1 medications work by significantly reducing your appetite, which means you are eating less. And when you eat less, you take in fewer nutrients. In fact, a 2026 narrative review published in Clinical Obesity found that more than 60% of adults on GLP-1 therapy consume below estimated requirements for calcium and iron — and vitamin D intake averaged just 20% of daily recommendations (Kreider et al., 2025). Meanwhile, testosterone therapy increases metabolic demands on the body, making certain nutrients even more critical for optimal results.

At Concierge Medical Clinic, we believe that medication is only part of the equation. Here is our evidence-based guide to the most important supplements to take while on GLP-1 and testosterone therapy.

1. Creatine — Your Muscle’s Best Friend

Why You Need It

One of the most underappreciated side effects of GLP-1 therapy is muscle loss. Because GLP-1 medications suppress appetite so effectively, many patients are not consuming enough protein to maintain lean muscle mass. Research has compared the rate of muscle loss during long-term GLP-1 therapy to decades of age-related decline — a sobering statistic that makes muscle preservation a clinical priority (U.S. News Health, 2026).

Creatine is one of the most well-studied supplements in the history of nutrition science. It is a naturally occurring compound made from three amino acids — arginine, glycine, and methionine — that helps your muscles produce energy during high-intensity activity.

What the Research Says

A 2025 narrative review published in Obesity Pillars specifically examined dietary supplement considerations during GLP-1 therapy and found that creatine supplementation can preserve lean mass while building muscle strength during weight loss — particularly when combined with resistance training (Kreider et al., 2025). For TRT patients, creatine works synergistically with testosterone to promote muscle protein synthesis and strength gains, making it doubly important for men on hormone therapy.

How to Take It

• Dose: 3-5 grams of creatine monohydrate daily
• Timing: Any time of day — consistency matters more than timing
• Form: Creatine monohydrate is the most researched and cost-effective form
• Note: You may notice a slight increase in scale weight initially due to water retention in the muscles — this is normal and not fat gain

2. Vitamin D — The Hormone-Like Vitamin You Are Probably Deficient In

Why You Need It

Vitamin D is not just a vitamin — it functions more like a hormone in the body, regulating hundreds of processes including immune function, bone health, mood, and critically for our patients — testosterone production and metabolic health.

Studies consistently show that Vitamin D deficiency is extremely common, affecting an estimated 42% of Americans. In Florida we get plenty of sunshine but sun exposure alone is often insufficient, especially for patients who work indoors or use sunscreen regularly.

For GLP-1 patients, the problem is compounded. When you are eating less food, you are taking in less dietary Vitamin D — and a 2026 review confirmed that GLP-1 users average only 20% of the recommended daily Vitamin D intake from diet alone (Kreider et al., 2025).

Vitamin D and Testosterone — A Critical Connection

The relationship between Vitamin D and testosterone is well established in the literature. A landmark study published in Hormone and Metabolic Research found that men who supplemented with Vitamin D had significantly higher testosterone levels compared to placebo after 12 months of supplementation (Pilz et al., 2011). Low Vitamin D is consistently associated with lower testosterone levels — making supplementation essential for men on TRT and those considering it.

What the Research Says

A 2025 peer-reviewed narrative review confirmed that Vitamin D supplementation can fill nutrient gaps from dietary intake, increase suboptimal serum levels, and offer long-term health benefits for patients on GLP-1 therapy (Kreider et al., 2025).

How to Take It

• Dose: 2,000-5,000 IU of Vitamin D3 daily for most adults
• Timing: With a meal containing fat — Vitamin D is fat-soluble and absorbs best with dietary fat
• Pair with: Vitamin K2 — helps direct calcium to bones rather than arteries
• Test first: Ask your provider to check your Vitamin D level (25-OH Vitamin D) — optimal range is 50-80 ng/mL

3. Fish Oil (Omega-3 Fatty Acids) — The Anti-Inflammatory Powerhouse

Why You Need It

Fish oil is one of the most versatile and evidence-backed supplements available, and it is particularly important for patients on both GLP-1 and testosterone therapy for several compelling reasons.

GLP-1 medications reduce food intake significantly — and most patients on these medications are simply not eating enough fatty fish to meet omega-3 requirements. Omega-3 fatty acids are essential — meaning your body cannot make them — so they must come from diet or supplementation.

Benefits for GLP-1 Patients

• Cardiovascular protection — GLP-1 therapy causes rapid weight loss which can temporarily stress the cardiovascular system. Omega-3s have well-documented cardioprotective effects
• Reduces inflammation — weight loss itself triggers inflammatory pathways. Fish oil counteracts this systemic inflammation
• Improves insulin sensitivity — directly supports the metabolic goals of GLP-1 therapy
• Supports muscle health — reduces exercise-induced muscle soreness and supports recovery

Benefits for TRT Patients

• Reduces cardiovascular risk — testosterone therapy can modestly affect lipid profiles. Fish oil directly addresses this by lowering triglycerides
• Supports joint health — testosterone therapy increases training capacity and fish oil reduces joint inflammation
• Anti-inflammatory — supports overall metabolic and hormonal health

What the Research Says

A 2026 evidence-based supplement guide confirmed that omega-3 fish oil at 1-2g EPA/DHA daily reduces inflammation, supports cardiovascular health, and may improve insulin sensitivity — making it one of the most beneficial supplements for GLP-1 users (GLP-1 Nutrition Lab, 2026). A 2025 narrative review in Obesity Pillars also specifically listed omega-3 fatty acids as a recommended supplement during GLP-1 therapy to fill nutritional gaps and support long-term health outcomes (Kreider et al., 2025).

How to Take It

• Dose: 1-3 grams of combined EPA/DHA daily
• Timing: With meals to improve absorption and reduce fishy aftertaste
• Form: Look for supplements that list EPA and DHA amounts specifically — not just total fish oil
• Quality matters: Choose molecularly distilled fish oil to minimize heavy metal contamination

Bonus Supplements Worth Considering

While creatine, Vitamin D, and fish oil are our top three, here are additional supplements worth discussing with your provider:

Magnesium — supports over 300 enzymatic reactions, muscle function, sleep quality, and testosterone production. Most Americans are deficient.

Vitamin B12 — GLP-1 therapy can reduce B12 absorption. Deficiency causes fatigue, brain fog, and nerve damage.

Protein Supplementation — not technically a vitamin but critically important. GLP-1 patients often struggle to meet daily protein requirements. Aim for 0.7-1g of protein per pound of body weight daily.

Zinc — essential for testosterone synthesis. Deficiency directly lowers testosterone levels.

A Word of Caution

Not all supplements are created equal. The supplement industry is largely unregulated, meaning the quality of what you buy matters enormously. Look for supplements that are:

• Third-party tested — NSF Certified, USP verified, or Informed Sport certified
• Free of proprietary blends — you should know exactly what and how much you are taking
• Manufactured by reputable companies with transparent ingredient sourcing

Always discuss any supplements with your provider before starting, especially if you are on prescription medications. Some supplements can interact with medications or affect lab results.

The Bottom Line

GLP-1 therapy and testosterone replacement therapy are powerful tools — but they work best when your body has the nutritional foundation to support them. Creatine protects your muscle mass, Vitamin D supports your hormonal health, and fish oil fights the inflammation that can undermine your results.

At Concierge Medical Clinic we take a whole-person approach to your care. If you have questions about which supplements are right for you based on your labs and health history, we are here to help.