From another website: "Even if you assume complete absorption by the partner, a large amount of semen, and a very highly concentrated drug present in the semen, researchers believe the resulting transfer is unlikely to be clinically significant." In short, not enough drug in not very much semen and not very long in your body to absorb it, equals not a big amount to be passed on to you. But if you partner is high, be sure you are being careful about protection, for birth control and preventing STDs.