Retatrutide + TRT + Tadalafil: Popular Stack, Zero Combined Trials
Each of the three has real trial data on its own. Nobody has published a study of the three together, so the stack is three separate evidence bases, not one.
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What Each Piece Is Meant to Do
A weekly GIP, GLP-1 and glucagon receptor agonist. In the phase 3 TRIUMPH-1 trial (2,339 adults with obesity, no diabetes), mean weight change at 80 weeks was -23.7% on 9 mg and -25.0% on 12 mg, against -3.9% on placebo. It is still investigational.
The usual reason for adding TRT to a weight-loss drug is to protect muscle. In one 100-man RCT of obese men with low testosterone on a very low energy diet, testosterone undecanoate cut fat mass by 2.9 kg more than placebo by week 56. It did not prevent muscle loss during the diet itself: both groups lost similar lean mass over the 10-week diet (-3.9 vs -4.8 kg, P=0.36). The 3.4 kg lean mass advantage at study end came from men on testosterone regaining lean mass during the 46-week maintenance phase.
A PDE5 inhibitor taken once daily at 2.5 or 5 mg. Pooled data from six placebo-controlled trials (1,913 men) showed IIEF erectile function scores rising by 4.2 and 5.4 points over placebo. Obese men reached a clinically meaningful change only on 5 mg.
A meta-analysis of 24 studies found that losing weight raised total testosterone in obese men, and the amount of weight lost was the best predictor of the rise. That matters for a stack that already contains a strong weight-loss drug.
What the Data Shows
Which Combinations Have Actually Been Studied?
| Pairing | Closest published evidence | Strength |
|---|---|---|
| Retatrutide + TRT + tadalafil | No trial found on PubMed. The "most common stack" label comes from a social media list, not a study. | None |
| Retatrutide + TRT | No retatrutide trial. Nearest: a 10-man pilot adding testosterone undecanoate to tirzepatide in hypogonadal men (5 per group). | Very low |
| Retatrutide + tadalafil | No published trial or interaction study found. | None |
| TRT + daily tadalafil | TADTEST, a 173-man placebo-controlled RCT: adding testosterone to daily tadalafil helped only men starting at or below 3 ng/mL. | Moderate |
Key Takeaways
- No published trial has tested retatrutide, TRT and tadalafil together. We found no PubMed record pairing retatrutide with testosterone or with tadalafil.
- Retatrutide alone produced -23.7% (9 mg) and -25.0% (12 mg) mean weight change at 80 weeks in TRIUMPH-1, with gastrointestinal effects the most common adverse events.
- In the phase 2 trial, retatrutide raised heart rate in a dose-dependent way; the rise peaked at 24 weeks and declined after.
- In TRAVERSE (5,246 men with low testosterone and high cardiovascular risk), testosterone gel was noninferior to placebo for major cardiac events (7.0% vs 7.3%) but had more atrial fibrillation, acute kidney injury and pulmonary embolism.
- In the TRAVERSE sexual function substudy, testosterone improved sexual activity and desire but not erectile function. That gap is the usual argument for adding a PDE5 inhibitor.
- In TADTEST, adding testosterone to daily tadalafil improved erections only in men whose baseline testosterone was 3 ng/mL or lower. Above that, it added nothing over placebo.
- Whether retatrutide changes how TRT or tadalafil behave in the body. No interaction study has been published.
- Whether TRT protects lean mass during retatrutide weight loss. The only incretin-plus-TRT data is a 10-man tirzepatide pilot.
- Whether men who lose 20%+ of body weight on retatrutide still need TRT, since weight loss itself raises testosterone.
- Long-term safety of running all three at once, including the heart rate rise from retatrutide alongside TRT's atrial fibrillation signal.
- Which approach works best for obese men with low testosterone. A 23-trial network meta-analysis found no single strategy consistently superior, with low or very low confidence in many comparisons.
Frequently Asked Questions
Is retatrutide + TRT + tadalafil a proven stack?
No. It is popular, not proven. A widely shared X post called it the most common stack, but we found no published trial combining retatrutide with testosterone or with tadalafil. Each drug has its own trial data, and only TRT plus daily tadalafil has been tested together in a randomized trial (TADTEST, 173 men).
Why do people add TRT to retatrutide?
Mostly to hold on to muscle during fast weight loss, but the evidence is narrower than that claim. In a 100-man RCT, testosterone undecanoate did not reduce lean mass loss during the 10-week very low energy diet: both groups lost similar amounts (-3.9 vs -4.8 kg). Men on testosterone regained more lean mass over the next 46 weeks, ending 3.4 kg ahead of placebo at week 56. That trial used diet, not retatrutide. A retatrutide substudy in people with type 2 diabetes found the share of weight lost as lean mass was similar to other obesity treatments.
Does weight loss on retatrutide raise testosterone by itself?
It may. A meta-analysis of 24 studies in obese men found that weight loss raised total testosterone, and the amount lost was the strongest predictor. Bariatric surgery produced about three times the rise of low-calorie diets. No study has measured testosterone changes on retatrutide specifically.
Does TRT fix erectile dysfunction on its own?
Not reliably. In the TRAVERSE sexual function study of 1,161 men with low testosterone and low libido, testosterone gel improved sexual activity, desire and hypogonadal symptoms over two years, but did not improve erectile function compared with placebo.
How long does daily tadalafil take to work?
Longer than people expect. In TADTEST, erectile function kept improving for at least 12 weeks on tadalafil 10 mg once daily, and the authors concluded the full benefit may take that long. In six pooled trials, 5 mg daily raised IIEF erectile function scores by 5.4 points over placebo at 12 weeks.
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Retatrutide is an investigational drug and is not approved by the FDA. Testosterone and tadalafil are prescription medicines. Talk to a licensed clinician before starting, stopping or combining any of them.
This page summarizes published research. It is not a protocol or a dosing recommendation.
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