Drugs and alcohol
The use of intoxicants is against the fifth precept, and given that the lack of a clear mind is one of the most fundamental problems with human flourishing according to Buddhism, it would not seem sensible to add to delusion and ignorance (and possibly cause more greed, desire and hatred) by drinking or taking drugs. Many Buddhists, not only monastics, completely renounce alcohol and other drugs. However, some argue that the problem is using alcohol/drugs to excess rather than at all. It sometimes depends on local culture, for example, drinking beer is traditional in Tibet and Mongolia. Nothing was said by the Buddha about smoking tobacco, so some Buddhists have smoked, but in the light of recent knowledge of its harmfulness, many would no longer see it as acceptable.