Does the drug omeprazole lessen the effect of loestrin birth control? During sex the condom broke and I am worried that the drug may have lessened the effect of my pill.

This site says, yes, it lessens the effectiveness of oral contraceptives - http://drugs.emedtv.com/drugs-articles-a-to-z-page-2.html

I can not find any direct statement about any interaction from the drug manufactor. On several other question and answer sites, it appears that writers have stated their doctors have also warned about interaction issues.

You need to discuss this with your doctor to see if he feels there is a issue.

Of course as you know, no one form of birth control is 100 percent effective, so even if not effected, there is always a chance a pregnancy.

You will just have to wait till time for your next period and see.