Anything wrong with the placebo effect? No. As a matter of fact, I am in favor of it. Your mind can heal your body better than drugs can, and the more you believe, the better it works, so why not believe?
The problem with believing in Zamzam water without basing it on scientific placebo controlled studies is that we appear delusional, naive and we are not likely to use the placebo effect in its correct way. We might waste valuable time, money and effort securing Zamzam water from far-off places when there can be more effective treatments (placebo or material) readily available.
German physician Dr Knut Pfeiffer studied Zamzam water, but through listening to this interview and googling his research, I found no consideration by him of the placebo response.
It’s OK to lie to ourselves when we are desperate for a miracle, but when we are not, we need to be more objective and realistic.
Not only are we being unscientific, we are being un-Islamic when we believe that Zamzam water has miraculous powers. Aren't we asked to use our minds and not take anything on faith unless we have proof?
Zamzam water was not mentioned in the Quran, so how can we have blind faith that it has miraculous powers? The Quran asserts in numerous ayahs that miracles don't happen anymore. This happens to be an issue of creed so we need unequivocal and conclusive evidence to believe in it.
As for the Sunnah, the following are hadiths that mention Zamzam water:
"إنها مباركة. إنها طعام طعم" مسلم
"Indeed it is blessed, and that like food, it fills." (Muslim)
And in Abu Dawud's narration, there is this addition:
"وشفاء سقم" (زيادة في رواية أبي داود)
"And a cure for illness." (Abu Dawud)
But that can be said of any water. The ayah says,
"وَنَزَّلْنَا مِنَ السَّمَاءِ مَاءً مُبَارَكًا فَأَنْبَتْنَا بِهِ جَنَّاتٍ وَحَبَّ الْحَصِيدِ" (ق، 9)
"We have sent down blessed water from the sky and irrigated with it gardens and seeds" (50:9)
The following hadith is considered weak by many Hadeeth scholars, but even if you consider it strong, it supports the argument that the effect is nothing but a placebo that is activated by intention.
"ماء زمزم لما شرب له، إن شربته تستشفي به شفاك الله، وإن شربته لشبعك أشبعك الله به، وإن شربته ليقطع ظمأك قطعه الله، وهي هزمة جبريل وسُقيا الله إسماعيل" الدارقطني والحاكم
"Zamzam water is for whatever you drink it for. If you drink it with the intention of being cured, Allah will cure you. If you drink it to satisfy your hunger, Allah will satisfy your hunger. If you drink it to quench your thirst, Allah will quench your thirst. It was dug by Jebril and is the water with which Allah quenched the thirst of Ismail." Ad-Daraqutni and Al-Hakim
I look forward to the day when I can drink Zamzam water and imagine myself being healed by it, but until then, I will drink filtered tab water and imagine myself being healed by it.