I often hear that people who are taking antibiotics experience wild fluctuations between feeling full of energy and completely alert but soon after feeling impossibly fatigued and sick.

Does this have anything to do with the antibiotics being used by the body as anything? For example as a hormone or as a source of nutrition? Is this this a reported side effect when used for other infections?

  • 2
    $\begingroup$ Mono is caused by the Epstein-Barr virus. The antibiotics won't do anything to fight against that, anyway. Sometimes antibiotics are given to fight the strep throat infection that can accompany mono. $\endgroup$
    – jonsca
    Commented Jan 28, 2012 at 3:23
  • 1
    $\begingroup$ ah didn't know that. Well, they tell me its mono... haha $\endgroup$ Commented Jan 28, 2012 at 5:25
  • 1
    $\begingroup$ can't really answer this, but I wanted to mention that there are some stimuli that can make you feel full of energy. There are anecdotes that drinking some radioactive isotopes also make some people feel great. See "The Great Radium Scandal" by Roger Macklis in the August 1993 issue of Scientific American. $\endgroup$
    – shigeta
    Commented Jul 27, 2012 at 16:53

2 Answers 2


I have never heard about this phenomenon from my patients or professors at the Medical School, but this is a possible mechanism that comes to my mind.

One of the classification for antibiotics takes consideration the effect on bacteria. Two possible effects are either stopping the proliferation (and letting the immune system to kill those that are currently present in the body) or killing bacteria directly.

The second approach is obviously more effective but has one big disadvantage: massive death of bacteria leads to the massive release of their toxins that are normally trapped within they bodies (so-called endotoxins). The symptoms you describe as "impossible fatigue" match exactly the symptoms of bacterial intoxication -- and this can increase upon the antibiotics intake.

Depending upon the bioavailability and pharmacokinetics some antibiotics might not kill all bacteria "on the first run" and the symptoms of intoxication recur several times with decreasing severity of manifestations.

  • $\begingroup$ Over the years since this question was posted, gut flora research has become mainstream. Could the elimination of gut flora cause a statistically significant increase of nutrients in the blood stream? Could that be a source of the proposed effect? $\endgroup$ Commented May 11, 2018 at 16:07

"There are antibiotics which contain carbohydrates, such as Gentamycin and Streptomycin (the aminoglycosides). These must be the antibiotics that could account for this phenomenon."

My conjecture that the carbohydrate moities contained within aminoglycosides account for the high energy is incorrect. Aminoglycosides are NEVER metabolized by the body, they are excreted out into the urine UNCHANGED. See here: http://www.ebmedicine.net/topics.php?paction=showTopicSeg&topic_id=43&seg_id=839

And even if it were possible to metabolize the carbohydrate molecules within them, the energy released would be far less than the energy consumed to break their linkages in the first place, thus placing a negative energy balance on the body, and thus, not providing the burst of energy that is apparently observed after taking antibiotics.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .