Ivermectin usually can't get to the brain [2, 8]. This is because the barrier between the blood and the brain stops it from doing so [2, 8, 9]. In particular, a small pump on this barrier called 'p-glycoprotein p' makes sure that any ivermectin that does get into the brain is forced back into the blood [2, 8, 9]. However, if this pump doesn't work (for example, if it is focusing on another drug) or if there are small holes in the barrier (which can happen during infection), ivermectin might get into the brain [2, 8].

If ivermectin does get into the brain, it can target something called a GABA-A receptor [10, 11]. When GABA-A receptors are stimulated under normal circumstances, they bring about an anti-anxiety effect that can calm the neurons and stop them from getting over-excited [10, 11, 12]. However, ivermectin can stop these receptors from working properly; it causes lots of chloride ions to rush into the neurons [10, 11, 12].

• This means that other neurons are more likely to fire rapidly, because GABA can't tell them to stop or slow down [11, 12].

  • • This is why people who have taken too much ivermectin might have seizures, as the neurons in the brain get too excited and work too quickly.

• Furthermore, lots of GABA receptors are found in an area of the brain called the cerebellum - this usually helps us with our balance and coordination [13].

  • • When GABA receptors here are affected by ivermectin, the cerebellum might not be able to function properly.

    • This might lead to lots of the brain-related overdose symptoms - like a loss of balance and coordination, as well as dizziness.

The brain controls what your muscles do. It tells them when to move, and when to stay still. As such, if ivermectin gets into the brain, the dysfunction it causes in the neurons can affect our ability to control our muscles. So, ivermectin can make someone feel like they can't control their muscles or have muscle spasms.

This may also be linked to a theory that suggests that ivermectin can inhibit another type of receptor in the brain and spinal cord called a glycine receptor [14, 15]. Like GABA, these receptors work to calm down surrounding neurons and stop them from getting over excited [15]. Glycine receptors are found all over the body and can help nerves to control the muscles, sense pain, and detect sights and sounds [14, 15]. So, if glycine receptors were inhibited, ivermectin overdose patients might have uncontrolled muscle movement or spasms, an increased response to pain or sensitivity to light and sound.

Some suggest that ivermectin can inhibit another type of receptor in the brain and spinal cord called a glycine receptor [14, 15]. When these are inhibited, many patients feel dizzy or nauseous, or have pain in their tummy. Some may even vomit or have diarrhoea [14, 15]. Some scientists think that this is a common response to toxins in the body, as our body recognises a potential danger and tries to work to expel it [16].

Furthermore, ivermectin may affect the bladder and bowels too. When the brain and the nervous system is disrupted by ivermectin, the signals the brain sends to the bladder & bowels to empty might become mixed, lost, or more frequent. Often, they are so strong that the person cannot voluntarily override this signal (like we normally can when we cross our legs!). As such, disruption of the nervous system might be the reason that ivermectin overdose patients lose control of their bladder and bowel.

Ivermectin overdose is associated with low blood pressure, also known as hypotension [1, 5]. This is often accompanied by symptoms like fainting, blurry vision, confusion, and loss of consciousness [17].

If the blood pressure becomes dangerously low, the heart may try to pump faster to circulate enough blood around the body [18]. A very fast heart rate is another common symptom of ivermectin overdose [1, 5]. If the heart pumps over 100 beats per minute in an adult that's resting, the person is said to be tachycardic [19]. If the person remains tachycardic for a long period of time, the heart's electrical system might fail, and the person may suffer a cardiac arrest [20]. This can lead to death [20].