Unpacking Pain Relief: How Does Paracetamol Work?

Paracetamol, also known as acetaminophen, is one of the most widely used painkillers in the world. Yet despite more than a century of use, exactly how it eases pain has remained something of a scientific puzzle. New research is now shedding light on the answer, and it points to an unexpected place: the body’s own cannabinoid system.

At a Glance: How Does Paracetamol Work?

• Paracetamol is a widely used painkiller and reduces fevers, but exactly how it works is still not fully understood.
• Scientists have traditionally believed that it works by blocking enzymes in the brain involved in producing pain signals, helping to reduce pain without significantly reducing inflammation.
• More recent research suggests paracetamol may also interact with the body’s endocannabinoid system, which helps regulate pain, mood, and other physiological processes.
• Studies indicate that paracetamol may reduce the production of the endocannabinoid 2-arachidonoylglycerol (2-AG), influencing cannabinoid (CB1) receptor activity and contributing to its pain-relieving effects. However, researchers are continuing to investigate this mechanism.

The Mystery of Paracetamol’s Action

Whether it is a headache, a cold or general aches and pains, paracetamol is often the first thing people reach for. It was introduced into UK hospitals in the 1950s, yet scientists are still piecing together exactly what happens when we take it. What is clear is that paracetamol works primarily in the brain and central nervous system.

Experts initially believed that paracetamol primarily worked by blocking certain enzymes called cyclooxygenases (COX) in the brain, similar to how anti-inflammatory drugs work. However, paracetamol has minimal effect on inflammation which is why it cannot relieve all types of pain.

This theory has been challenged because paracetamol typically needs to reach much higher concentrations than are seen at normal therapeutic doses to inhibit COX enzymes directly. This has led scientists to explore other possible mechanisms, including how paracetamol interacts with the body’s endocannabinoid system. This system involves natural compounds (endocannabinoids) and special receptors found throughout the body and brain, playing a role in regulating various functions, including pain.

This may help explain why paracetamol can relieve pain affecting different parts of the body, even though the primary location of action for paracetamol is the central nervous system where CB1 cannabinoid receptors are most abundant. Researchers are continuing to investigate the precise role these receptors play in paracetamol’s pain-relieving effects.

Hypothesis: N-arachidonoylaminophenol (AM404)

An earlier proposed mechanism for paracetamol’s action involved one of its breakdown products called N-arachidonoylaminophenol (AM404). It was hypothesised that paracetamol is converted into AM404, which then acts on the endocannabinoid system by blocking the reuptake of the endocannabinoid anandamide or inhibiting its breakdown by the enzyme fatty acid amide hydrolase (FAAH). This could lead to increased anandamide levels, potentially activating cannabinoid receptors (CB1, CB2) or TRPV1 channels to produce pain relief.

However, the concentrations of AM404 typically achieved in the body after a standard paracetamol dose appear to be too low to explain these effects. In fact, one study found that AM404 did not alter cannabinoid signalling in a neuronal model used to test direct effects of paracetamol. Despite this, experts continue to consider how the paracetamol interacts with the endocannabinoid system beyond AM404.

New Discoveries: Paracetamol and the Endocannabinoid System

A recent study published in Cell Reports Medicine looked closely at how paracetamol interacts with the endocannabinoid system. The researchers found something unexpected: Paracetamol seems to inhibit an enzyme called diacylglycerol lipase alpha (DAGLα).

Why is this important? DAGLα is responsible for creating a specific endocannabinoid called 2-arachidonoylglycerol (2-AG). When DAGLα activity is reduced by paracetamol, it leads to less 2-AG being produced.

This might seem counterintuitive because many endocannabinoids, including 2-AG, are often associated with reducing pain. However, the study suggests that in some situations, reducing 2-AG production by inhibiting DAGLα might actually help relieve pain.

Key Findings from the Research

The study used various laboratory techniques, including tests on brain cells and mice, to understand paracetamol’s effects. These are some of the key takeaways:

• Paracetamol reduces 2-AG synthesis: Experiments showed that paracetamol significantly decreased the production of 2-AG by inhibiting DAGLα. This effect was observed at concentrations of paracetamol that are relevant to the amounts found in the body during therapeutic use.
• CB1 receptors are involved: The pain-relieving effects of paracetamol in mice were dependent on CB1 receptors. When these receptors were blocked or absent, paracetamol did not provide pain relief.
• DAGL inhibition also relieves pain: The researchers also found that directly inhibiting DAGL with another compound also reduced pain in mice, and this effect also required CB1 receptors.

These findings suggest a new model for how paracetamol works: it might reduce pain by inhibiting DAGLα, which in turn reduces the activation of CB1 receptors in specific pain pathways.

Does Paracetamol Block Pain Receptors?

Rather than directly blocking pain receptors, paracetamol is thought to relieve pain by changing how pain signals are processed in the brain and central nervous system. Researchers believe this may involve the body’s endocannabinoid system, including cannabinoid (CB1) receptors, although the exact mechanisms are still being investigated.

Paracetamol and Cannabis: What do Patients Need to Know?

While there are typically no major pharmacological interactions between cannabis and paracetamol, medical cannabis patients should always inform their doctor of any other medication they are taking. It’s important to stick to the recommended doses for each and to consult your specialist if you have any concerns or experience any side effects.

What Does the Function of Paracetamol Mean for Understanding Pain?

This research provides exciting new insights into the complex ways pain signals are transmitted and interpreted in the body. It highlights that the endocannabinoid system, particularly the interaction between DAGLα and CB1 receptors, could be a key player in pain signalling.
While more research is needed, especially in humans, these findings open doors for potentially developing new pain relief treatments that target DAGLα. This could lead to more effective strategies for managing various types of pain in the future.

This study reinforces the intricate role of the endocannabinoid system in our health and how different medications might interact with it to produce their effects. As research continues, these findings may also help inform the development and understanding of other treatments that target the endocannabinoid system, including medical cannabis.

Disclaimer: This blog post is based on scientific research conducted in laboratory settings and animal models. While the findings are promising, further studies are necessary to fully understand their implications for human health and clinical pain management.