I am listening to the book Surviving Schizophrenia and in the book, it is mentioned that drugs like Clozapine increases in blood level if the patient takes Caffeine, and can have side effects due to elevated levels. In case the patient takes Caffeine, can't just less amount of Clozapine work since it'll be significant enough to help the patient and cause less side effects too? I am not from a medical background, sorry if these things are pretty obvious in medical community

  • $\begingroup$ Welcome to Biology.SE! Please take the tour and then go through the help pages starting with How to Ask questions effectively on this site and edit or delete your question accordingly. In particular note that personal medical questions are not appropriate for this site. No matter how good your (and our) intentions are, relying on health information from people who aren't medical professionals is unwise and could be extremely dangerous. Thanks! 😊 $\endgroup$ – tyersome Nov 12 '20 at 22:59
  • $\begingroup$ In general, since everyone metabolizes caffeine and clozapine differently, it would be extremely hard to make sure that the patient got the right dose. It's easier to say "stop using caffeine while on this". Grapefruit juice does much the same thing; makes it harder to break down drugs, doctors do not say "drink grapefruit juice and we'll halve your dose". They say "avoid grapefruit juice". $\endgroup$ – swbarnes2 Nov 15 '20 at 20:11
  • $\begingroup$ The place to ask about medical topics is SE Medical Sciences. Here the focus is on defined biological mechanisms, rather than complex diseases and the varying effects of drugs. $\endgroup$ – David Nov 20 '20 at 16:45

I used Google Scholar with the search terms of clozapine, caffeine.

I only found small scale studies, but they agree that it is likely that Clozapine levels are affected by caffeine intake.

To really understand the implications of this it would be necessary to research what the range of Clozapine levels actually are in patients and what the effective level is, as well as the levels that give side-effects.

Only then can the changes due to caffeine be seen to be significant or not

Example paper studying 12 volunteers below (full text available)

Hägg, S., Spigset, O., Mjörndal, T. and Dahlqvist, R. (2000), Effect of caffeine on clozapine pharmacokinetics in healthy volunteers. British Journal of Clinical Pharmacology, 49: 59-63. https://doi.org/10.1046/j.1365-2125.2000.00111.x Available at:


  • $\begingroup$ Your DOI link is incomplete. $\endgroup$ – MattDMo Nov 12 '20 at 19:33

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