Do Antibiotics affect performance?

So I’m currently on antibiotics and am also failing workouts left, right and centre. Is this linked? The antibiotics are for a dental problem so the illness on its own shouldnt affect things too much.

If antibiotics do mess up things what’s the best way to manage it?

Ramp test and do prescribed workouts at lower intensity? Stick to Z2? Stay off the bike till the course of antibiotics is over? Give up cycling forever and take up fishing?

A lot of people feel they do but the reality it is probably the more the infection that is knocking you off your game


The guys were talking about antibiotics and their effect on training and performance in Podcast 75, I suggest you give it a listen.

Ask a Cycling Coach - TrainerRoad Podcast - Ask a Cycling Coach: 075 - TrainerRoad Podcast on Stitcher

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Running rather than cycling, but …

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Its like the article is about me…

“The horse who normally cantered a morning run at about 25mph dropped instantly to 15mph on the same loop, with the same perceived effort, while on antibiotics.”

Thanks for the help - doesn’t seem like its all in my head.


I had 2 dental implants placed and was told to take a course of antibiotics. I had no active infection. my performance suffered pretty good shortly after beginning the antibiotics and lasted for maybe a week after I finished up the course. Was it a result of the antibiotics or the stress/recovery from the dental implants, i don’t know. That’s my N=1.


I have to take antibiotics daily and have been for several years. I’m stronger than ever and am setting PRs on the bike.

My issue is I feel absolutely horrible when off antibiotics, and it really impacts my training. A healthy person may have different results, but for me my overall performance improves when I’m on antibiotics and not feeling so bad.

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I imagine a lot depends on the type and the dose. Low dose amoxicillin, for example, will be very different to high-dose metronidazole…


I don’t think you can still assume that. Just because the infection would be considered minor or be located in an area that doesn’t contribute to pedaling a bike doesn’t mean the rest of your body won’t be affected. Also, as mentioned above, the affect of an antibiotic on your body (and thus performance) can vary depending on the specific antibiotic as well as the dose as they have different side effects and mechanisms of action.

As for recommendations. I would personally stick to Zone 2 for a week but most of all just listen to your body.


Metronidazole 3x 400mg a day :man_shrugging:

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Well known for making you feel like poo.

And if you have a dental abscess (total guess, could be wrong), your body will perceive that as a systemic problem; put them together and I’m not surprised you’re failing workouts.

Do Pettit and maybe some easy outside work, then I’d personally go back to where you were the week before things went south and re-assess from there.

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I took a course of amoxicillin last fall for a sinus infection and felt terrible for the whole course. Legs were sore even with a much reduced training volume. I had a Pettit+1 ride and HR was like +20 over usual.

+1 for its the infection not the antibiotics

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Hi Coke,

are you really on a permanent treatment? Never heard of that. How come?

I am currently on AB in order to kill off the Helicobacter Pylori, that thing in the stomach which can cause ulcers and gastritis.

Was more or less off the bike for 4 weeks with some easy commuting (300km) when I started the treatment consisting of 2 different AB and 2x6 pills of them (plus another two meds. So a total of 18 pills a day.).

It is safe to assume that I have no infection slowing me down. Don‘t know how mich the FTP can drop, but now I am at start of SSB2 5% below my first testresult upon starting SSB1 in Nov.

The trouble are not the legs, but that my body is really struggling much more to absorb oxygen.

Yes. It’s the only thing that has worked for pouchitis.

I am currently in week 2 of 4 weeks of Bactrim. I missed one workout due to the illness and then subbed in Pettit for a few days. First hard day back and I say I was 5-10 watts off but I put this down to the illness more than the antibiotics, but it is impossible to say if it is illness, antibiotics, training interruption, mentality or regular variation. I feel totally fine and was able to complete 2 of the 3 hard workouts this week, will report back if I can see any impact going forward. Currently I am at the end of specialty so maybe the decreased volume covers up some of the potential impact of the antibiotics.

How long did it take after you finished your course of antibiotics to get back to normal? I’m in the same boat, stepped it down to zone2 with plenty of rest. Off the bike I feel great on the bike RPE is thought the roof and my legs are burning like I’m doing VO2 repeats. Hopefully I finish this course and can get back at.

Don’t think I quite got back to normal. The week on antibiotics was rough… low energy and sore legs. Here’s a calendar link for me at the time: - TrainerRoad
I was missing workouts left and right. I think the “sinus infection” annotation is the 10 day course of amox/clav I took. It was the last 6 weeks of cx season, so partly I was trying to ensure I’d at least be rested to race on the weekends. I did pull out a good cx states race shortly after (carried a peak?), but the next few races definitely were underperformed even though I was sort of getting my workouts back on track.

This thread is somewhat of a relief. Just bailed from Baird+2 (3x 5xVO2) without even completing the first set, notes say “Didn’t have it today”. I’m currently on antibiotics after root canal treatment at the weekend, but assumed that they’d have no effect so was worrying about stress, diet etc.!

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