Tequila no matter what type (blend, 100% agave, butros) all are plant derived, where most other alcohols are grain or even fruit based. For some people this has a big effect on how their body takes it. Like some other answers here stated, they can drink whisky, vodka, scotch with no problem, but tequila screws up thier bodies metabolism, and or stomach. Plant based alsohol does have a different string of impurities compard to a grain spirit. You have heard stories of how some people become totally different when under the influence of tequila, this is very true to me. I am an avid sour mash, single malt, or blen and I am fine, and just the smell of tequila makes me nausous. The way the body absorbs tequila does vary compared to another form of distilled spirits, and this will cuase different reactions. If tequila does effect you in a negative wat, just steer clear, and go with something more soothing.
Matt B is right on the money here, except for his percentages but he still deservers your "best answer".
I will add that the impurities added to non-100% agave tequila are largely sugar based and ANYTIME you mix liquor and sugar in excess you will feel far sicker than with just the alcohol alone.
In order to be labeled "tequila" under Mexican law (ALL tequila is produced in Mexico) it has to be at least 51% agave. Poorly made ones like most versions of Cuervo & Sauza are indeed right at this percentage, so it's barely half "real" tequila.
Cuervo only makes 2 good tequilas that bear it's name; Tradicional & Reserva de la Familia. 1800 is their's too, and are decent, but (thankfully) don't say Curevo anywhere on them. Sauza only makes 1 100% tequila (that I know of as I avoid Sauza) which is under the name Hornitos, but it's still not a very good one.
Since you specifically asked about tequila & vodka, I would criticize Kevin's answer as both tequila and vodka are plant based and thus his argument doesn't really hold up.
Good tequila (NOT Cuervo, Mezcal) will not make you sick...i.e. hungover, etc. Good tequila is made form 100 % Agave. Cuervo and others use very little agave, and mostly corn sugar. That's why it tastes like crap. Cabo Wabo, Petron and others are very easy drinking, and very easy on the stomach. Tequila that is 100% Agave is required to be 100% Agave. Otherwise it can be as little at 40-10% Agave. The less Agave, the worse it is. I have some 100% Agave tequila that I pour in a glass, neat, and sit and sip while watching t.v. and I like just as much as JD Single Barrel.
different alcohols have different effects on different people. I can drink basically everything until i cant walk and never get sick. But there are certain alcohol that i stay away from too because i cant tell just by the smell that i will vomit if i drink it. Tequila is one, along with burbon & rum. My hubby can drink most things but 'girly' drinks make him sick and also if he mixes drinks. Like if he drinks beers then swapa and has vodka or liquer, he gets really sick.
the impurities. Vodka (especially high quality vodka) has very few imurities in it. Tequila has a ton.
Also everyone has different reactions to different alcohols. I can't drink gin to save my life, but I can down a bottle of Irish single malt whiskey and feel absolutely fine the next day.
tequila feel sick vodka