Without going down a rabbit hole here, the word meditation is often used in different ways by different people, and refers to different practices. In the west, meditation is often used to mean deep reflection or deep thinking. Think of Marcus Aurelius' Meditations, or the 12-Step Daily Meditations. In the east, meditation (in particular classic Buddhist meditations) is used to observe reality clearly as it is unfolding. So any intoxicant (which alters our perception) naturally would not be seen as helpful. Mantra meditation is a bit different - a substance could be seen as helpful, at least from the devotional traditions. So it all really depends on the type of meditation you are doing, your reasons for doing it, and how far you want to go in your meditation.
Ram Das had a neat story he used to share. He went to India to find a meditation teacher, and (it being the 1960's) took a vial with a bunch of liquid LSD with him. When he found his teacher, his teacher said "give me the medicine" (Ram Das hadn't told him he had anything on him) and then ingested the entire vial. He then asked Ram Das to sit and meditate with him. After meditating through the night, the teacher finally turned to Ram Das and said, "we have this sort of medicine too. Meditation is better."