Can drug abuse cause memory blackouts?

Hello doctor,

I have a 23 year old son. He admits to current marijuana use once or twice a week. He admits to a variety of drugs including cocaine, meth, heroin, LSD in the past year. His ex-mother in law says he currently uses cocaine and meth. He denies current drug use beyond pot. He says he has not done cocaine for a few months. He swears he is only currently using pot occasionally now and no other drugs. I realize he may be lying. In the last month, he has had several extended blackouts where he was fully functioning, walking around town, having conversations with people, damaging property, etc. Sometimes friends cannot wake him, and they think he is having a seizure. He does not remember drinking any alcohol on that day. In fact, he has no memory of that day, until waking up at home. Everyone told him about the events the next day. He has no memory of these events. Some are as short as an hour. Some are as long as 48 hours or more. I live 6,000 miles away from him and flew in this week to see him. I only have a few days with him to try to convince him to see a doctor, and I am trying to see if this is just drug use, him lying, being in denial or if there is a severe neurological condition that is not being treated because everyone is assuming he is on drugs. He has a history of serious sleepwalking when he was a child. He would rush out of his room, frantically searching for something but unable to describe it. He would carry on whole conversations, very agitated, would go outside, walk around the house and come to the back door crying and try to get in but be unable to turn the knob. It was like a walking nightmare or dream. We would get him back to bed and back to sleep. The next day he would have no memory of it. This current behavior sounds similar to me but on a much more extreme level. His sister had night terrors similar to this when she was a child. I, as their biological father, have a history of talking in my sleep, and some sleepwalking when I was a child but never this extreme. So, there seems to be some family history as a possible explanation outside of drug use being the probable cause. He sleeps very little. His current girlfriend says he is extremely sleep deprived. He lived with me until a few months ago and was extremely sleep deprived then. I realize you cannot give a definitive answer without personal examination and tests and such. What I am looking for right now is the answer to these three questions. Cancocaine and meth use actually result in these kinds of fully functional blackouts? Can just marijuana, (without any other drugs) or just alcohol or just marijuana and alcohol, combined with sleep deprivation and extreme stress cause these kinds of blackouts? Are there any other possible explanations for this kind of blackouts that are not drug related, for example, sleep deprivation and stress, a tumor, or other neurological or medical conditions? What might some of those possibilities be? Thank you for your help. I am distraught and confused.

Thank you doctor,

I also remembered he fell five months ago and hit his head and was diagnosed with a concussion. I think that is the only other detail I may have neglected. Does that make any difference? I admit I was surprised to hear that marijuana alone can explain this level of a blackout behavior. In my youth, I overused alcohol and had some strange blackout stories told to me as well. People recognized me as being drunk though. Some of the descriptions he is receiving during his blackouts are that he seemed coherent though agitated. Friends finding him clammy, unable to wake him, and thinking he is having a seizure, do all those fit with transient global anesthesia (TGA) from excessive marijuana use as well? He freely admits marijuana use but, may be downplaying how much and how often he uses it to me. He repeatedly states 'pot is not dangerous' to me and I keep saying I think it is. So, thank you for that confirmation. It is my understanding that cocaine and meth metabolize and leave the system fairly quickly. Is there an over the counter test (at a local drug store) that would show me if coke or meth has been used if it has been more than three or four days? Do any of those tests indicate an amount of marijuana in his system or just a yes or no answer rather than a level? He has agreed to see a counselor. I will try to get him to agree to let me have a session with the counselor so that I can share what I am aware of.