I missed my contraceptive pill yesterday. Is it safe to take two pills on the same day?

If you missed a pill then sometimes it is recommended to take two pills in one day. Taking the two pills at least 10 hours apart should not be a problem. Taking them closer together could make you a little nauseous, and you do not want to throw up after taking the pills.
If you want to take regular contraceptive pills as emergency contraception, you might take 2-4 at once. If it has been more than 24 hours since your last pill, use a second method, like a external condom (male) or internal condom (female) anytime you have sex for the next 7 days.