The idea of a Xenomorph Royal Jelly was first proposed by Bishop in Alan Dean Foster's novelization of the film Aliens. As how Xenomorph hives resemble those of Earth's bees, the Alien Queen's Royal Jelly acts in much the same way as a queen bee's, namely nurturing drones and workers into a queen should the original queen perish. In comics, Royal Jelly made its first official appearance in the first issue of 1991's Aliens: Genocide.
Royal Jelly is essential for Xenomorphs to propagate their race, as without a Queen, they can birth no more of their kind, and the jelly is the only way to create a new Queen without one being directly birthed by the old Queen. Xenomorphs are therefore highly protective of their hive's jelly. If someone or something attempts to steal it, any Xenomorphs within the area will be alerted by their Queen and report to her in order to eliminate the thief. Royal Jelly is specific to hives however, and only the Xenomorphs from the hive of the jelly's origin will react positively to it. Any outside Xenomorphs will recognize the pheromones of jelly, but if it is not of their hive then it is considered to be of an enemy, as anything unfamiliar is considered a threat. Although humans already tend to be killed on sight by Xenomorphs, if said human came into contact with an opposing hive's Royal Jelly, then there will be no way for them to escape the unrelenting rage of the Xenomorphs, as they are highly attuned to tracking pheremones and Royal Jelly carries some of the most potent pheromones of any substance known to Xenomorphs. In Aliens: Music of the Spears, a fully restrained Xenomorph is shown to react so harshly to a single vial of Royal Jelly being sold in a drug deal that it resorts to killing the humans that came into contact with it by repeatedly ramming them against a wall, as it had no way to free itself in order to attack them.
While Royal Jelly is a purely Xenomorph substance, it can also have a range of effects on humans. It can essentially act as a performance enhancer, temporarily increasing a person's speed, strength, and reaction time; it can also give an intense feeling of well-being and competence, allow a person to become aware of things normally beyond their perception, and some can even experience what seems like a never-ending orgasm. While the overall effects vary from person to person and depending on the potency of the jelly, essentially, Royal Jelly is like crack cocaine on crack. Withdrawal symptoms are nothing short of severe.