Has mastubation a bad effect?

Yes & no. It is a normal healthy thing. Anything to excess can be bad for you. Most times if you redirect your thoughts, it can keep you from over doing it. You want to train your body to respond to stimulation when it suits you, not it controlling you.
I know guys who have over indulged and then at an old age, they have erectile disfunction.

Ask ur doctor

When you masturbate you are becoming intimate only with yourself. This may lead you to not wanting to become intimate with some one you care for because the sexual encounters do not produce the satisfaction you receive when masturbating. Because we know how to satisfy ourselves better than someone else can. You need to have good communication with your partner and perhaps show your partner what pops your top. Include some of your masturbation techniques as foreplay. This way you get your orgasm and you get the intimacy and closeness we all crave from some one we love.

Masturbation like any other thing you can get addicted to. If you find yourself always wanting to masturbate rather than meeting the opposite sex or the same sex if you're gay than you may need some help. Most people like to masturbate when there frustrated or really horny to relieve stress and urges. Its a safer way to satisfy your "needs" than having sex all the time if you're still a teenager.

Here is a web site with discussions and questions answered all about it. You might want to check it out. http://www.ismasturbationbad.com/main.htm