Woodworking, not only with power tools, but even with hand tools, can be a dangerous activity. Even the slightest lapse in judgment can result in a devastating injury. Safety should always be first and foremost in the woodworker's mind. As such, the woodworker needs to be alert and attentive in the wood shop.
One way to help insure an alert and attentive mind is to avoid alcohol and drugs (of any kind) when woodworking.
While it isn't uncommon for construction workers or "weekend woodworkers" to pop a few beers while working with power tools, it is not a good idea. Having a buzz while using a potentially deadly piece of equipment is a recipe for disaster. Save the alcohol for the end of the work day, but make sure that you've completely gotten it out of your system before you start your woodworking the next day. Working hungover and tired can be just as disastrous as drinking while woodworking.
Drugs are no different. I've heard of many an injury from a person using one type of pill or another to help them keep going at the end of a very long day. This is another recipe for disaster.
However, prescription drugs can be just as dangerous. If you are concerned that a prescription pharmaceutical may be interfering with your ability to keep a clear mind, discuss it with your doctor. Don't be afraid to tell him/her that you are a woodworker and are concerned about keeping your wits about you when working in your shop.