Short answer

Mixing alcohol and smoked cannabis increases impairment beyond what either drug does alone. Both substances slow reaction time, affect balance, raise heart rate, and weaken the gag reflex. Effects from a hit of THC start in 5 to 10 minutes and last 2 to 3 hours. Alcohol effects last longer. The liver clears one standard drink per hour, at about 0.015% blood alcohol concentration per hour.

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What the combination does to the body

Heart rate and blood pressure

THC can raise heart rate by 20 to 50 beats per minute. Alcohol widens blood vessels and lowers blood pressure. Together they can cause a fast pulse, flushing, and a blood pressure drop when a person stands. The result is dizziness and fainting. Falls while intoxicated cause head injuries and fractures.

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Nausea and vomiting

Alcohol irritates the stomach and triggers vomiting at high doses. THC can cause dizziness, nausea, and vomiting, a set of symptoms called greening out. Alcohol is a central nervous system depressant. At high doses it weakens the gag reflex. Vomit that enters the airway causes aspiration, which is a medical emergency.

Effects of Using Cannabis with Alcohol on the Body

THC levels in blood

A study in Clinical Chemistry found that alcohol raised plasma THC levels when participants vaporized cannabis. Peak THC concentrations were higher with alcohol than without it. Higher blood THC also matters for drug tests and for states with per se THC driving limits.

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Liver enzymes

THC is broken down by CYP2C9 and CYP3A4 enzymes. Alcohol is broken down by alcohol dehydrogenase and, at higher doses, CYP2E1. The pathways overlap in part. Clearance rates differ by person, dose, and frequency of use.

Edibles

Edibles take 30 to 120 minutes to produce effects and peak later than smoked THC. That delay extends the window when alcohol and THC both act on the body.

Timeline

Alcohol peaks in blood 30 to 90 minutes after a drink. Smoked THC peaks in plasma 5 to 10 minutes after a hit. Smoking while drunk puts the THC peak on top of a rising or near-peak blood alcohol level. Impairment from both drugs overlaps for 2 to 3 hours. Residual effects on attention and balance can last longer.

Risks

Driving

Crash studies link the combination of alcohol and cannabis to more impairment and more crashes than either substance alone. Most states set a per se alcohol limit of 0.08% BAC for drivers 21 and older. Utah sets 0.05%. Some states also set THC limits, such as 5 ng/mL of THC in whole blood. A medical cannabis card is not a defense for impaired driving.

If someone is unwell

  1. Stop the drinking and the smoking.
  2. Move the person to a safe spot and have them sit or lie on their side.
  3. Give water if they are awake and can swallow.
  4. Stay with them.
  5. Call 911 for chest pain, slow or irregular breathing, seizure, unresponsiveness, or vomiting during sleep.

What does not help

Coffee, cold showers, and energy drinks do not lower blood alcohol or reverse THC effects. CBD does not cancel the impairment from alcohol or THC. Time is the only thing that clears both drugs.