Does smoking decrease effectiveness of birth control and increases pregnancy risk?

No. The smoking would increase your risk of adverse effects from the medication, not pregnancy.
No. However smoking increases the risk of blood clots while on birth control pills, as well as many other health risks.
Smoking. Smoking will not cause your oral contraceptive to be less effective. However, a woman who smokes & uses oral contraceptives can have increased risk for heart attack, stroke, and blood clots. Smoking does increase risks if you are pregnant.

Related Questions

I've been on cefprozil antibiotic and take my birth control everyday at the same time. I also use the pull out method. Pregnancy risk?

No. There is very little pregnancy risk when a woman is taking birth control pills properly, and is not having vomiting nor diarrhea. That coupled with the pull-out method, means almost no chance of pregnancy. However, life can be full of surprises. That means any fertile woman having sex must be already prepared to get married, settle down, and raise a family, in the event of a surprise pregnancy. Read more...

What is the pregnancy risk of having unprotected sex with my girlfriend who is on birth control (never misses a pill) and has amenorrhea (due to pill)?

Unprotected/oxymoron. An oxymoron is a statement that contradicts itself on its' face. If your girlfriend is consistently taking the oral contraceptive pill, then she is protected from pregnancy from sexual encounters, but not from STD's if a condom is not used. Her risk for pregnancy is less than 0.1%. Read more...

If I am between 5-6 hours late taking birth control pills 2x and had protected and then unprotected sex with no ejaculation what is my pregnancy risk?

Low pregnancy risk. If you were 5-6 hours late taking your birth control pills twice and if you are otherwise taking your birth control pills every days, the chance of pregnancy is quite low. To have a chance of pregnancy you would probably need to be 12-24 hrs late. That being said, it is safest to take your bcp about the same time every day. Read more...

Sex on the first day of the 7 day placebo pills (birth control pills), started the new pill pack 2 days late. Is there a pregnancy risk from that particular encounter? (1st day of a 7 placebo period

You tell me..... during the placebo interval you are supposed to have a normal period. If you did, then there is very little chance of conceiving during that period. If you did not... then... all bets are off. Read more...
No. You are protected by the hormonal suppression of the active ingredients in the pill and the timing of your recent intercourse. Read more...