Red Bull cans litter trails used by people moving north.
Folks move constantly out in the desert--during the day and through the night--walking for miles and miles, elevation changing in feet by the hundreds in relatively short distances, temperatures fluctuating sometimes in excess of fifty degrees between day and night, with periods of rest most likely short and far between.
With little food, and little sleep, keeping energy up must be a primary issue of concern.  There is no respite for folks who are slower than the rest of the group.  In many instances, if a person is too slow, they are left behind, alone.
Being left alone can be deadly.  Without a guide many people are lost, and can wander for days without seeing a house or a frequently traveled road, or another person.  Even if they manage to stay on trails, avoid being robbed, avoid dehydration, exposure or injury, they still have no recourse for reaching their destination.  Most people don't know where they are going--told by their guide they are only a day or two from their destination--they often ask how far L.A. is, or Phoenix, or state their intention to walk to Tucson, without knowing it is sixty miles north.
With a guide, a group will often walk to a prearranged pick-up point, far enough north to avoid checkpoints on local roads or the interstate.  From there, groups are taken to wait, or are held, in safe-houses in area cities, such as Tucson, until a van going east, or west or north, to L.A., or New York, or Wisconsin or North Carolina is ready to go.
Being left behind by a group leaves people without options, without any knowledge of where they are, where they can go, or how to contact someone if they even make it out of the remote desert.
So keeping up is essential, and many folks drink Red Bull while crossing--either by choice or after being given it by their guide to help them keep up.
This presents problems.  Red Bull is straight caffeine and sugar.  It gives a very significant boost in energy and is followed by a very significant drop in energy when the effects wear off.  It also increases heart rate to abnormally high levels.  During periods of physical strain--such as walking for days in the mountains of southern Arizona--a person's heart rate is already raised.  Combined with the effects of Red Bull, a person could easily show signs and symptoms of hypertension--chest pain, shortness of breath, even disorientation.
Red Bull, as all caffeine, is a significant diuretic too--causing increased urine output.  In these circumstances when water intake is already minimal, these drinks compound the chances of serious dehydration.
Aside from the negative side effects, the intended effect of Red Bull--a boost in energy--is also dangerous.  Folks are already moving at fast speeds when they cross through--moved along quickly by their guides, from a distance, a group of people might look like they are jogging together.  Having the energy to move faster than one should, or is comfortable moving, is dangerous, as the ground gives easily on steep inclines of loose rock and sand--another source of sprained ankles, twisted knees and other debilitating injuries that leave folks stranded, alone.
There is never a balance for people moving north, nor ever a chance for a balance.  It is a constant struggle with, among other elements, time, weather, orientation, ground conditions, piercing vegetation, poisonous animals, border enforcement agents, guides, hunger, thirst, dehydration, exposure, hypothermia, darkness, the sun.