THC can cause impairments in short- and long-term memory. What is the evidence that these can be reversed by caffeine?
Memory deficits are one of the most common side effects of cannabis consumption. THC can impact multiple types of memory. Two of the most important are episodic memory and working memory. Episodic memory is what most people think of as long-term memory and working memory is what most people think of as short-term memory.
Caffeine is the world’s most popular psychoactive drug (sorry, cannabis only lands at #4 after both nicotine and alcohol). Naturally, many people who consume cannabis will also consume caffeine at the same time. Since many people believe that caffeine improves memory, this brings up an important question: can caffeine reverse the memory deficits of cannabis?
On the surface, it seems like the answer would be yes. However, what I found was that it all depends on which type of memory we are talking about.
The Basics of Caffeine Pharmacology
Before I get into what happens when you combine with cannabis, how does caffeine work on
its own? Caffeine works through a neuromodulator called adenosine. The adenosine system actually has a ton of similarities to the endocannabinoid system. It’s receptors are expressed widely throughout the brain and they regulate the function of many other neurotransmitter systems.
Adenosine has 4 receptors: the A1, A2A, A2B, and A3 receptors. Caffeine is an antagonist of all of them. Since adenosine causes drowsiness, caffeine will cause alertness by blocking the effects of adenosine.
Notice that I said in the introduction that “many people believe” caffeine improves memory. In reality, the effects of caffeine on memory are mixed. Some studies have shown that caffeine can improve memory, other studies have shown it has no effect. This can depend on the study subjects used, the dose of caffeine, the type of memory being tested, and even the time of day.
One thing that caffeine does for sure is increase alertness, especially in people who are otherwise tired. Alertness and attention are important for formation and recall of memories.
Caffeine May Improve Long-Term Memory Deficits from THC
Let’s look first at the effects on long-term memory. A 2017 study examined how blocking a specific adenosine receptor could reverse deficits in episodic memory in mice. They didn’t specifically test THC, but rather a CB1 agonist that acts in a similar way to THC.
Mice were allowed to explore an object and then were given the CB1 agonist. The next day, the mice were tested to see if they remembered exploring the object. As expected, the CB1 agonist appeared to impaired the mouse’s memory of the object.
Next, the researchers administered an antagonist of the adenosine A2A receptor (either every day for 30 days or a single dose was given at the same time as THC). Blocking the adenosine A2A receptor completely reversed the deleterious effects of THC on long-term memory formation. Since caffeine also blocks the adenosine A2A receptor, I expect that it could have similar effects.
Caffeine May Worsen Short-Term Memory Deficits from THC
A 2011 study looked at how THC and caffeine interact in short-term working memory in rats. The rat’s short-term memory was significantly worsened by THC in a dose-dependent manner (meaning that higher doses of THC resulted in a stronger effect on memory). This was no surprise, since these results have been seen previously in both rodents and humans.
In rats who received a high THC dose, caffeine had no effect – it neither improved nor worsened short-term working memory.
However, something surprising happened when caffeine was combined with a low dose of THC (a dose low enough to have no effect by itself on short-term memory). Adding caffeine to the low dose of THC actually made memory performance worse. In fact, memory performance of the low dose THC + caffeine group looked a lot like the rats who received a high dose of THC.
This memory-worsening effect of caffeine was mimicked by an adenosine A1 antagonist, but not by an adenosine A2A antagonist. This shows that the adenosine receptor which makes short-term memory worse is different from the adenosine receptor which makes long-term memory better.
Recommendations for Combining Caffeine and Cannabis
Overall, the net effect of caffeine on your memory while you are high is probably beneficial. Caffeine counteracted the deficits in long-term memory induced by THC. So if you want to better recollect what you were doing while high, then drink some coffee at the same time.
Some people find health benefit in low doses of THC that are not very psychoactive. Be warned that if you consume caffeine at the same time as the low-dose THC, it may impact your short-term working memory as much as if you consumed a full dose of THC.
A huge caveat of all of this is that it is based on studies in rodents and it has not yet been confirmed in humans. Of course, if you just want to drink coffee for the sake of drinking coffee and don’t have anything intellectually demanding to do, then it doesn’t really matter. There aren’t any known negative health effects of combining caffeine and cannabis. Most caffeinated beverages are high in anti-oxidants and the latest research says that coffee will actually extend your life!
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