As Halloween approaches, the air fills with excitement. Costumes are planned, pumpkins are carved, and the promise of sweet treats is everywhere. But while dipping into chocolates and colourful candies may seem harmless, some ingredients in these festive favourites can cause trouble for people taking certain medications or living with specific health conditions.
Author
- Dipa Kamdar
Senior Lecturer in Pharmacy Practice, Kingston University
From artificial sweeteners to liquorice and chocolate , Halloween sweets can interact with medicines or worsen some conditions in ways that may reduce their effectiveness or even trigger harmful side effects . Here's what the science says, and why you might want to glance in your medicine cabinet before raiding the treat bowl.
1. Chocolate
Chocolate treats are everywhere this time of year, but for people taking monoamine oxidase inhibitors (MAOIs), one of the older types of antidepressant, they can carry unexpected risks. MAOIs are usually prescribed when first line antidepressants have not been effective . These drugs work by blocking an enzyme in the body called monoamine oxidase, which helps control levels of brain chemicals linked to mood. When this enzyme is blocked, it also prevents the breakdown of a natural substance called tyramine , which is found in certain foods such as chocolate, cheese and cured meats.
When someone on MAOIs eats tyramine-containing foods such as chocolate, tyramine can build up to dangerous levels. This can cause blood vessels to tighten, leading to a sudden and severe spike in blood pressure , which is a medical emergency that can be fatal if untreated.
Exactly how much chocolate is risky depends on the dose and type of MAOI, as well as the kind of chocolate and your individual sensitivity. There's no universally "safe" amount, but even small portions of dark chocolate , which contains more tyramine, can sometimes cause problems. Milk chocolate usually contains much less tyramine, but doctors generally advise caution or avoidance altogether, especially during the early stages of treatment or at higher doses. If in doubt, it's safest to check with your pharmacist or prescriber before indulging.
2. Caffeine
Chocolate also contains caffeine, a stimulant that can interact with medicines used to treat attention-deficit hyperactivity disorder (ADHD), anxiety, and heart problems.
Caffeine and ADHD drugs such as methylphenidate (Ritalin) are both nervous system stimulants , although they work in slightly different ways. Together they can intensify each other's effects, leading to jitteriness, insomnia, and a racing heartbeat. This can make it harder to manage ADHD symptoms effectively.
Caffeine may also reduce the calming effects of antidepressants and anti-anxiety medicines such as selective serotonin reuptake inhibitors (SSRIs). It can raise blood pressure and heart rate, which may cause problems for people taking beta-blockers for heart conditions.
A 50-gram bar of dark chocolate usually contains less than 25 milligrams of caffeine , while milk chocolate contains less than 10. That might not seem much, but when combined with coffee, tea, or energy drinks, caffeine intake can quickly add up. The Food Standards Agency advises that up to 400 milligrams a day is unlikely to cause side effects for most adults.
However, the safe limit during pregnancy is much lower: no more than 200 milligrams a day (about two cups of instant coffee). Exceeding that has been linked to increased risk of miscarriage and low birth weight . Sensitivity to caffeine can also vary depending on health conditions, medications, and individual metabolism, so people taking heart or mental health drugs may need to be especially cautious.
3. Liquorice
Liquorice is the ultimate love-it-or-hate-it treat. But if you're a fan, it's best to eat it sparingly. Black liquorice contains glycyrrhizin , a natural compound that acts like the hormone aldosterone . This can cause the body to hold on to sodium and lose potassium , leading to fluid retention, increased blood pressure and electrolyte imbalances.
These effects can be especially dangerous for people taking diuretics, antiarrhythmic drugs, or blood pressure medication, and for those with kidney disease. Even small amounts of liquorice can make a difference. A 2024 study found that just 100 milligrams of glycyrrhizic acid daily can raise blood pressure. That is the same as the upper limit recommended by the World Health Organization . If you have a heart or kidney condition, it's safest to avoid large amounts altogether. Liquorice-flavoured sweets that do not contain real liquorice are usually fine.
4. Artificial sweeteners
Sugar-free sweets are often marketed as healthier, but they can come with their own risks. Many contain artificial sweeteners such as aspartame , which can be dangerous for people with phenylketonuria (PKU), a rare genetic disorder. Aspartame breaks down into a chemical called phenylalanine, which people with PKU cannot properly metabolise. This leads to a toxic buildup that can damage brain cells .
Phenylalanine may also be indirectly converted into tyramine, which means that consuming aspartame might contribute to higher tyramine levels. Like chocolate, this could interact with MAOI antidepressants and cause a dangerous rise in blood pressure, although more research is needed to confirm this link.
5. Food colourings
Halloween sweets are known for their bright colours, but those vibrant hues often come from synthetic dyes such as Red 40, Yellow 5, and Blue 1. These dyes have been linked to hypersensitivity reactions including hives, wheezing and itching. One study found that people who are allergic to aspirin may be more likely to react to Yellow 5.
For anyone taking antihistamines, these dyes can make things worse. They don't clash chemically with the medicine, but they can trigger the body to release histamine - the very substance antihistamines are meant to block - or provoke allergic reactions of their own. To make matters worse, some antihistamines also contain artificial dyes, so the treatment can end up feeding the problem.
Research has also found a connection between artificial food colourings and increased hyperactivity in some children.
A few sweets won't ruin your night, but if you take medication or have a medical condition, it's worth being mindful. Read ingredient labels, go easy on chocolate, sugar-free sweets, or liquorice and check with your doctor or pharmacist if you are unsure.
After all, the scariest part of Halloween should be the costumes, not what's hiding in your sweets.
Dipa Kamdar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.
