Rav Avigdor Nevenzahl שליט״א, one of the foremost students of Rav Shlomo Zalman Auerbach זצ״ל, and former Chief Rabbi of the Old City once told me that if not for the possible legal issues that may come from it, it would not just be allowed, but it would be a mitzvah to steal, take away from, and ultimately destroy your friends' cigarettes from them, as it has been proven without a shadow of a doubt that smoking leads to cancer.
With this in mind, it seems obvious to apply that if you were to give your cigarette to your friends, though not officially transgressing lifnei iver biblically (as they could acquire their own from the local store around the corner) it would be prohibited rabbinically.
Therefore best to just get rid of them.