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Pause Reta for half marathon training

13 replies7 peopleOct 4, 2025☆ Follow
Summary

Does retatrutide reduce energy for long endurance runs and should it be paused during half marathon training?

The original poster experienced sudden bonking on a 15k after three weeks on 0.5 mg Reta despite normal fueling, unlike a prior half marathon. They paused the drug and later completed their race with better energy, then resumed at a micro-dose while reducing long runs. Others reported similar fatigue and elevated heart rate on Mounjaro or Reta during runs over 8 miles, with recovery taking weeks after stopping; one cyclist noted improved fat oxidation at 2 mg.

What this discussion establishesWhere people disagree

Some attribute the issue to insufficient fueling while others link it directly to the medication's effect on glucagon or heart rate.

Still open

Whether Reta raises heart rate or lowers VO2 max during exertion remains unconfirmed by the group.

Nothing here is advice.

13 replies · 7 people
NorthWillow50archiveopening postOct 4, 2025

I've been on Reta for three weeks at 0.5 mg weekly while building mileage for a half marathon. On last week's 15k I ran out of energy in the final miles, something that never happened when I ran a half in March. I used a hydration vest, pre-run electrolytes, a sandwich, and gels during the effort but still hit the wall. I'm wondering if low glucagon is limiting fuel for 1-2 hour runs and am thinking about stopping until after the mid-November race.

WrySparrow78archiveOct 4, 2025

Pausing seems reasonable. At that low dose it should clear quickly so you can test whether it was the cause.

CopperSignal33archiveNov 10, 2025

I had the same problem early this year while training for a marathon on Mounjaro: bonking on longer runs and higher heart rate. It took about four weeks to feel normal again after stopping. I'm considering trying Reta now as I start training for Tokyo in December, mainly just to finish given my knee issues.

KeenBramble46archiveNov 11, 2025

Stopping until it's out of your system is probably safest. Full saturation at your dose takes four weeks, but you could also wait and see if the low dose symptoms ease on their own.

NorthWillow50archiveNov 12, 2025

I went ahead and stopped. After more than four weeks the long runs feel good again; I did 12.5 miles recently. The race is this weekend and I'm feeling more confident about my energy. I'll post how it went afterward.

NorthWillow50archiveNov 29, 2025

I finished the half and ran the whole way. It was about ten minutes slower than my earlier one this year, but the weather was hotter and the course had a bridge climb. I also ran a 5k on Thanksgiving and set a PR. Last week I restarted Reta at a low micro-dose and I'm cutting back on long endurance work for now.

CopperFenwick68archiveNov 29, 2025

One Gu wouldn't be enough for me on a half, though I'm a slower runner. It might simply be a blood-sugar issue that needs more gels.

NorthWillow50archiveNov 30, 2025
↳ replying to @CopperFenwick68

I actually used three GUs and that worked fine: one at 30 minutes, another at 60, and the last around 90 minutes for a finish just over two hours.

CopperSignal33archiveDec 4, 2025

Good job finishing. Women often need different fueling amounts depending on the menstrual cycle. I've paced 2:10 races and run under 1:52; usually one gel plus some preload the days before is enough for me. I'm now on 0.5 mg Reta and will see how 10 miles go this Sunday. If energy drops like it did on Mounjaro I'll pause again for the next few months.

GreenFenwick93archiveDec 7, 2025

I'm doing endurance cycling on 2 mg weekly and have been able to extend unfueled rides, which I think comes from better fat oxidation in zone 2. I did make sure to eat extra carbs the day before long efforts. My old marathon fueling needs were much higher than what I use now on the bike.

AmberHarbour92archiveDec 8, 2025

Has anyone noticed changes in how heart rate feels on Reta and whether that affects race times? It seems resting or effort heart rate might be slightly higher, and I'm also curious about any impact on VO2 max.

CopperSignal33archiveDec 10, 2025

I'm only at 0.5 mg right now, mainly for food-noise control. Mounjaro gave me real HR trouble but so far Reta hasn't shown any effect.

NorthWillow50archiveDec 11, 2025

I haven't seen any HR change. I stay in lower zone 2 for training and my resting rate looks the same with or without Reta.

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Pause Reta for half marathon training · ZyraTrack Community