Involuntary intoxication is essentially a claim that someone else caused you to become intoxicated without your knowledge, and that you didn't willfully ingest drugs or alcohol.
This can be used as a defense for many crimes. For example, if you were accused of assault after starting a fight, but someone gave you drugs without your knowledge, you may claim that the drugs caused you to do things you would never have done sober. You may not even remember the incident and you can claim you didn't know what you were doing at the time.
From the standpoint of drunk driving, it often means that you were given alcohol that you didn't know about, putting you over the legal limit. When you got behind the wheel, you thought you hadn't had too much to drink and honestly believed your choice was both safe and in line with local laws.
For example, perhaps you went out to dinner. You had a drink with your meal, but, due to the hour you spent in the restaurant and the food you ate, you figured you were fine after just one drink. What you didn't know is that someone added alcohol to your drink right before you finished it off to go home.
When the police pulled you over, you blew over the legal limit, and you were just as shocked as anyone. The test showed that you had three or four drinks, but you only bought one.
This is just one example of how this defense can be used, but it shows you how it could be very realistic given the right set of circumstances. This defense is also sometimes used if pills -- like Rohypnol -- are slipped into a drink without the drinker's knowledge. If you think this has happened to you, resulting in DUI charges, you need to know your defense options.
Source: Cornell Law School, "Involuntary intoxication," accessed Dec. 22, 2016