I started taking Ocella a week ago. Is it enough time ( seven days) to start it to work ? or shall?

Providing the Ocella (drospirenone and ethinyl estradiol) pills are taken as directed below, they should be effective as a contraceptive after seven days.

From the Ocella product label:

DOSAGE AND ADMINISTRATION Oral Contraception
To achieve maximum contraceptive effectiveness, drospirenone and ethinyl estradiol tablets must be taken exactly as directed at intervals not exceeding 24-hours.
Drospirenone and ethinyl estradiol tablets consists of 24 pink active tablets of a monophasic combined hormonal preparation plus 4 inert white tablets. The dosage of drospirenone and ethinyl estradiol tablets is one pink tablet daily for 24 consecutive days followed by 4 white inert tablets per menstrual cycle. A patient should begin to take drospirenone and ethinyl estradiol tablets either on the first day of
her menstrual period (Day 1 Start) or on the first Sunday after the onset of her menstrual period (Sunday Start).

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Day 1 Start
During the first cycle of drospirenone and ethinyl estradiol tablet use, the patient should be instructed to take one pink drospirenone and ethinyl estradiol tablet daily, beginning on Day one (1) of her menstrual cycle. (The first day of menstruation is Day one.) She should take one pink drospirenone and ethinyl estradiol tablet daily for 24 consecutive days, followed by one white inert tablet daily on menstrual cycle days 25 through 28. It is recommended that drospirenone and ethinyl estradiol tablet be taken at the same time each day, preferably after the evening meal or at bedtime. Drospirenone and ethinyl estradiol tablets can be taken without regard to meals. If drospirenone and ethinyl estradiol tablet is first taken later than the first day of the menstrual cycle, drospirenone and ethinyl estradiol tablet should not be considered effective as a contraceptive until after the first 7 consecutive days of product administration. The possibility of ovulation and conception prior to initiation of medication should be considered.

Sunday Start
During the first cycle of drospirenone and ethinyl estradiol tablet use, the patient should be instructed to take one pink drospirenone and ethinyl estradiol tablet daily, beginning on the first Sunday after the onset of her menstrual period. She should take one pink drospirenone and ethinyl estradiol tablet daily for 24 consecutive days, followed by one white inert tablet daily on menstrual cycle days 25 through 28. It is recommended that drospirenone and ethinyl estradiol tablets be taken at the same time each day, preferably after the evening meal or at bedtime. Drospirenone and ethinyl estradiol tablets can be taken without regard to meals. Drospirenone and ethinyl estradiol tablets should not be considered effective as a contraceptive until after the first 7 consecutive days of product administration.