Grapefruit juice does not weaken the effectiveness of contraceptive pills. However, it can lead to an excessive increase in the concentration of hormones contained in birth control pills in the blood, and this can result in increased side effects.

This is due to the flavonoids and furanocoumarins contained in grapefruit, which can block the action of enzymes that metabolize certain drugs, including ingredients of contraceptive pills, as a result of which the concentration of these drugs in the blood increases.

In summary, the effect of birth control pills remains preserved, and there is no need for additional protection.

Below I have attached materials that may be of interest to you:

https://www.gdziepolek.pl/artykuly/jakie-leki-oslabiaja-skutecznosc-antykoncepcji

https://www.gdziepolek.pl/artykuly/czy-jedzenie-i-picie-obnizaja-skutecznosc-antykoncepcji