Mouth tape is a low-risk habit for the right person on a normal night. On a night you have been drinking, the risk calculation changes, and the simple, honest answer is: take the tape off. Here is why alcohol and mouth tape do not mix, and what alcohol is doing to your sleep either way. (The full mouth tape guide is here.)
Alcohol relaxes exactly the wrong muscles
Mouth tape is safe for a healthy adult partly because your body is a good self-monitor overnight — if breathing gets difficult, you rouse enough to adjust. Alcohol undermines both halves of that.
First, alcohol is a muscle relaxant, and it relaxes the muscles of the throat and airway. That makes the airway more prone to partial collapse and turns quiet sleepers into snorers — the airway is already more compromised before any tape is involved.
Second, alcohol is a sedative that blunts your arousal response. The gentle safety mechanism that mouth tape relies on — waking just enough to open your mouth if you need air — is exactly the reflex alcohol suppresses. You want that reflex sharp when your mouth is taped. Alcohol dulls it.
The nausea problem
There is a blunter reason too. Drinking raises the odds of nighttime nausea and vomiting, and a taped mouth is the last thing you want if that happens. This alone is enough reason to skip the tape on any night you have had more than a token amount to drink.
Alcohol is wrecking that night's sleep regardless
Worth saying plainly: even without the tape, alcohol degrades the sleep you are taping to improve. It helps you fall asleep faster, then fragments the back half of the night, suppresses REM, and — through that airway relaxation — worsens snoring and breathing. So a drinking night is not a night your mouth tape was going to rescue anyway. Taking it off costs you nothing.
The simple rule
Had a few drinks? Skip the tape tonight. Sleep normally, hydrate, and pick the habit back up the next night when you are sober and your reflexes are intact. A night off does not undo your progress — the nasal airway conditions over weeks, not single nights.
This is the same logic behind the other hard limits on mouth tape: do not tape when you are sick and congested, do not tape if you have untreated sleep apnea, and never tape during exercise. The common thread is simple — do not seal your mouth shut in any situation where your backup airway or your ability to react is compromised. (The full safety guide is here.)
The bottom line
Mouth tape depends on your airway being stable and your arousal reflex being intact. Alcohol degrades both. On drinking nights, take the tape off — it is the easy, obviously-right call, and you are not losing anything, because alcohol was going to disrupt that night's sleep with or without it.