It WILL be less effective that way, but not totally ineffective.

Have you guys considered birth control pills of some sort?

Condoms break, and BC pills are WAY WAY WAY more effective than condoms and plan B.

less effective yes but at lest there is something you can try and do.
but carifairy is right. if you feel ok with doing so you should ask your girlfriend about using a birth control. there is a lot more then just a pill that you take every day. there are rings, creams, foams, jells, patches, and IUDs, ect..

here is a like to look at if you'd like-
http://ehealthforum.com/health/topic100896 .html

Ok, thanks for all replies

Back to the BC pills and other BC alternatives, I'm not aware about them at all... I've heard something here and there, but it wasn't as much as I would like to know. I tend my girlfriend use BC pills, because we have sex almost everyday and some day 'that' can happen, but I'm worried whether it could risk her health... She has unregular period (probably because of stressful lifestyle), and always it is hard one... I mean all these pains near stomach area, etc., she always has to take pain relieve pills to fill little better... That's why I'm thinking BC pills aren't the best option for her. On the other hand it might get her period on the right track. I have no idea... I will look up the link which MyLove4U provided in his/her post. If you have any other advices, I will appreciate every single one. Thanks once again!

BC pills ARE HER BEST OPTION.

They REGULATE the period, STOP PAIN, AND make many women have easier periods.

Obviously you do not know much about birth control.

You both should make a visit to her gynecologist.

yeah, it sounds reasonable... thanks a lot!

ah ok. my husband was worried about the same thing. birth control pills will help her a lot with cramps and all. they will even make her period more predictable and regular. the pills work so that there is a leave of estrogen and progestin they are usually different for different colored pills, this is because they try tried to make the leaves as a real body would make hormones. so different parts of the month have different leaves.

also there is more then just a pill to take. like shots, patches, vaginal rings, IUDs, ect... the pill you have to remember to take everyday, the patch is once a week, the vaginal ring is 2 time a month (once to take it out and once to put it in) but they say it's once... whatever, the shot is 3 months, and others very.

there is always a risk with taking BC, blood clots are a really worry for women that smoke and are older. different bc act different. and you should really take to a doctor about that if she has any blood clotting problems and so on.

you'll have to pick through the kinds and see what works for you. what you should know is that how it all works is the hormone makes you not ovulate. meaning you don't release an egg every month but you do get your period like normal. some even thin the uterus wall so it's harder if there is a fertilized egg in there to be able to attach to the uterus. this also makes your period lighter.

like the other person said what you really need to do is go see her doctor. they will be able to help you pick something just right for her. if you need more info just ask.