Can you have too much serotonin?

Serotonin has an important function in our bodies, from regulating mood and appetite to influencing sleep patterns and sexual function. But can we have too much of a good thing? 

If you’re one of the eight million people in the UK living with anxiety or the one in six who have depression, it may be the case that you’ve considered talking to your GP about SSRIs (selective serotonin reuptake inhibitors). SSRIs are thought to work by increasing serotonin levels in the brain, which generally leads to a positive impact on mood.

But what are the implications when our serotonin levels are out of whack? We know they can be too low, but can we have too much serotonin, and what would this look like? We get the lowdown from medical experts. 

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What is serotonin?

Serotonin is a neurotransmitter – a chemical messenger – that sends signals between the nerve cells in the brain. As such, it’s involved in many bodily processes, as GP and founder of wellbeing platform Wellgood Wellbeing Dr Zoe Watson explains: “Serotonin is involved in a whole range of physiological processes, including sleep, memory and mood as well as appetite, gut motility and much more. Serotonin is synthesised in different regions of the body – it acts as a neurotransmitter in the brain, and as an intracellular signalling molecule outside the brain.”

Put simply – serotonin sends messages between the cells in our brain (the central nervous system) and our body (the peripheral nervous system). As such, it’s important that we have enough of it, so our body works smoothly and efficiently.

Serotonin is known as the ‘happy hormone’

As well as being a neurotransmitter, serotonin also works as a hormone.

“Most people know serotonin as the ‘happy hormone’,” explains Dr Watson, “as it is thought to be involved in regulating mood. In fact, the serotonin produced in the brain is implicated in the regulation of pretty much all human behavioural processes – and not just mood.”

You’ve probably heard of the gut-brain axis, and interestingly, 95% of the body’s serotonin is in fact produced in the gut, and only around 1–2% percent in the brain. The brain uses the amino acid tryptophan to create serotonin receptors, and we obtain this through our diet – most sources of protein such as nuts, dates, bananas and oats contain small amounts of tryptophan, although it’s widely thought that to be effective, these need to be consumed alongside a carbohydrate source.

But it’s important to note that the serotonin produced by the gut cannot cross the blood-brain connection, meaning in actual fact it has no direct impact on mood – but it does influence gut mobility, heart rate, breathing and more, meaning that while it’s important for overall health to have adequate levels in the gut, it’s the brain one that we’re really interested in here. 

What factors influence the levels of serotonin in the body?

This is complicated, as Dr Watson explains that “we can’t measure levels of serotonin in the living brain and serotonin levels fluctuate constantly depending on all sorts of factors, so even if you could measure brain serotonin, every single person would have a different amount depending on what they were doing at the time and what their general mental state is.”

However, we do know that serotonin levels are influenced by a complex interaction of environment, genetics and much more. “Mental health isn’t just about how low or high your serotonin levels are,” explains Dr Watson. “The important factor is the differing number, type and pattern of serotonin receptors within the different parts of brain.”

OK, so what happens when our levels are off? 

What happens when our serotonin is too low?

“Low levels of serotonin in the brain have been linked to depression, but the truth of this matter is that we don’t actually know if it’s that the low levels of serotonin which cause the depression, or if it’s the depression which causes the low-levels,” says Dr Watson. “In fact the serotonin theory of depression is one which is an ongoing area of research, and is frequently questioned by academics.”

Despite this, SSRIs are often the first line of treatment for depression, anxiety and mood disorders. They work by increasing serotonin levels in the brain, and while, as Dr Watson says, it’s oversimplifying matters to say that the issues being treated are caused by low serotonin, there’s no doubt that increasing our levels can improve symptoms.

What happens when we have too much serotonin?

Given that our levels of the hormone fluctuate according to so many different factors, if we are also taking SSRIs, is there a chance that we can end up with too much serotonin in our system?

The simple answer is yes – sometimes.

“One of the only scenarios in which we can have too much serotonin is when something called serotonin syndrome occurs,” explains Dr Watson. “Serotonin syndrome is generally a consequence of taking two medications, both of which increase levels of serotonin production within the brain.”

This might be the case if you’re taking more than one type of antidepressant at the same time, and it can cause some unpleasant symptoms.

“Serotonin syndrome can cause people to become agitated and sweaty, have diarrhoea, muscle twitching, confusion and raised body temperature,” warns Dr Watson. “It is a medical emergency and must always be treated in a medical setting.”

However, if your GP has recommended you take more than one medication containing serotonin, it’s likely they will have assessed the potential implications, and it’s always important to follow professional medical advice. 

Similarly, it’s never advisable to come off these kinds of prescribed medications without consulting your GP first. While potentially serious, serotonin syndrome is rare, but if you’re at all concerned about symptoms, speak to your GP.

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How can we regulate our serotonin levels?

Given the alternatives, it’s natural to want to keep our serotonin levels stable, but it’s not quite as simple as this.

“The truth is, that you can’t really regulate your serotonin levels specifically,” advises Dr Watson. “Like all neurotransmitters and hormones in our body, the processes which control serotonin release in both the gut and the brain are largely automatic.And it would be entirely impossible to do an activity that only influences serotonin levels without influencing levels of other hormones and neurotransmitters too.”

So, what can we do? We’re back to tried-and-tested techniques of maintaining good mental health: diet, exercise, good-quality sleep and so on. “Rather than focusing on how you can influence or regulate a specific hormone or neurotransmitter level, it’s better to focus on things we know are good for our overall mental and physical health, like any activities which increase your heart rate, eating plenty of fruit and vegetables, and spending time outdoors,” advises Dr Watson.

As always, if you’re struggling with low mood, depression or anxiety, do contact your GP for help and advice. 

Images: Getty

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