how do men last long with out ejaculating while participating in sex
in       x-rated movies? is it real or some kind of trick? or do they
take any medicine before they participate in sex?if so what kind of medicine?

I imagine masturbation right before followed by viagra would do it. 
Also, just like all movies, I imagine it can be done via editing. 
Sometimes you'll notice when the actors switch positions, they often
cut away.  While I don't know for sure, I imagine the actors could
rest for a bit during this period.

In addition, on some films, it seems that the cuts insert action from
an earlier stage of the "event".  You might also time the events shown
in films; I rather doubt that they actually last any longer than sex
between experienced partners.

There are a few different reasons for this. 

(1) They are professionals and have trained their bodies to achieve
orgasmic control, usually through long-term practice with masturbation
techniques such as the "Stop-and-Go" method. I found details on this
method on the following page:
http://sexeditorials.com/masturbation/male/stop-and-go.html

(2) Porn flicks, like many other movies, use special effects. Of
course, it's not the same type of special effects used in blockbuster
outer-space movies. However, repeating frames, lengthening scenes,
duplicating content, and other "tricks" are used in the business. For
example, even a basic website like http://advancedmasturbation.com can
cause the illusion of neverending masturbation movies to illustrate
the male techniques on the site. On that particular site, you can see
the film has been altered if you look closely.

(3) Although medications like Viagra usually aren't necessary to make
it look like porn stars can maintain an erection for hours, there are
some cheap over-the-counter medications that will prevent ejaculation
because of their effects on the central nervous system. The trick to
using these over-the-counter meds on a film stage is knowing how much
of a dose to use that will prevent the ejaculation yet still enable
the actor to get an erection. Too much will prevent an erection
entirely -- which is one reason why men aren't buying up all this
particular cheap over-the-counter medicine to last longer in bed. (I
won't mention the name of the medication that has this effect because
I don't recommend using them for this purpose. In addtion, sex does
not feel good while you're using it anyway. The penis gets all numb.)

Additional Information on Films:

(1) Although some films are realistic, most ejaculations in porn films
are also often fake, even though they may look real. Most men can not
shoot that much white semen.
(2) Yes, many men in porn films have larger (way larger) than average penises also!
(3) That's why it is a movie and not our real lives!

As someone who has been involved in the adult entertainment arena, I
can tell you that often times there is a process called "looping"
which consists of the same scene being played over and over.  So,
while it seems that the male actor is lasting a long time, it's
usually pretty normal, you're just watching the same action replayed.

having watched the larry david hbo comedy "curb your enthusiam"
episode where larry visits the house of an ex-porn star. I watched the
porn star confide in larry that taking a dab of hot sauce and sticking
it up the butt will help sustain an erection.

i know someone ( someone ) who attempted to simulate this result by
taking pepper cream  ( used for arthritis ) and putting it on the
perineum skin ( between the scrotum and the anus ). I've been told by
this person that it does cause an immediate errection but this
erection does not last nearly as long as the intense burning sensation
which cannot be mitigated with ice, soap, milk, or any other common
solution.
so don't burn your ballz off.

Most of the time these stars use medicine.There are some medicines and
enjection awailable specialy for the male stars.Anybody can buy from
the sex stores.A normal person can longer lasting only 4 to 5 minutes.