I took a drug test, but was on my 1st day of period, so blood mixed in urine, will it affect the results?

No: It should have no effect on the test for drugs.

Should be ok: A bit of blood should not interfere with the drug test. If there is any issue they will contact you for retesting. Good luck

Drug tests: Usually blood does not invalidate a drug test. I would read the insert if it was on a home drug test, or ask the technician if you had a test at a commercial testing lab to verify whether blood affects the readings. Usually the quality of tests are good enough that the readings stand on their own.