CoQ10 is generally well tolerated. Where side effects are reported, they're usually mild — most commonly digestive upset such as nausea or stomach discomfort, and occasionally headaches or difficulty sleeping. CoQ10 can interact with some medicines, including blood-thinning medication. If you take any prescription medication, or you're pregnant or breastfeeding, speak to a pharmacist or GP first.
CoQ10 side effects: what's actually reported?
If you're reading this, you've probably decided CoQ10 is interesting and you're now doing the sensible last check: is there any reason not to take it? Good instinct. Here's the honest picture — what's commonly reported, what's rare, who should check with a professional before starting, and how to begin sensibly. No scare-mongering, no breezy "it's all fine" either.
One framing note before we start: CoQ10 is a substance your body already makes and that's present in everyday foods like meat and oily fish. That's context, not a safety guarantee — "naturally occurring" doesn't automatically mean "no side effects for you". So let's look at what's actually reported.
The common (and usually mild) ones
CoQ10 is generally well tolerated in the amounts found in supplements. Where people do report side effects, the most common are:
- Digestive upset — nausea, stomach discomfort, reduced appetite, or loose stools in some people. This is the most frequently reported category.
- Headache — reported occasionally.
- Trouble sleeping — some people report feeling wakeful if they take CoQ10 late in the day. If that's you, taking it earlier — with breakfast or lunch — is the obvious first adjustment.
Two practical points that help: taking CoQ10 with a meal (which the label will usually say anyway, since it's fat-soluble) tends to be gentler on the stomach than taking it on an empty one, and if a product's daily serving is split across more than one capsule, spreading them across meals rather than taking them together can help too. Always follow the specific product's label.
The rare ones
More rarely, people report skin irritation or rash, dizziness, or irritability. As with any food supplement: if you notice something that concerns you after starting CoQ10, stop taking it and speak to a pharmacist or your GP. That's not small print — it's the actual right thing to do, and a pharmacist can usually tell you quickly whether what you're noticing is likely related.
Interactions — the part to take seriously
This is the section that matters most, and it's the one many CoQ10 pages bury. CoQ10 can interact with some prescription medicines. The ones to know about:
- Blood-thinning medication (anticoagulants such as warfarin). CoQ10 is structurally similar to vitamin K and may reduce how well some blood-thinning medicines work. If you take an anticoagulant, do not add CoQ10 without speaking to your pharmacist, GP or anticoagulation clinic first. This is the single most important line on this page.
- Blood pressure medication. CoQ10 may have additive effects alongside some blood-pressure medicines. If you're on one, check with a pharmacist before starting.
- Statins. You may have read that statins and CoQ10 are connected — statins can lower the body's own CoQ10 levels, which is one reason CoQ10 supplements get discussed alongside them. We're deliberately not going to tell you CoQ10 "helps" if you take a statin — that's a health claim no one in the UK is authorised to make, and the honest answer is that the research is mixed. What we will say: if you take a statin and you're considering CoQ10, that's a textbook "ask your pharmacist" conversation. It's free, it's quick, and it's specific to you.
If you take any prescription medication not listed here, the same rule applies: a two-minute conversation with a pharmacist beats any website, ours included.
Who should speak to a professional before starting
- Anyone taking prescription medication — especially blood thinners, blood pressure medication, or statins (see above)
- Anyone pregnant or breastfeeding — there simply isn't enough good data in these groups, so the careful answer is to ask your GP or midwife first
- Anyone with an existing medical condition or awaiting treatment
- Anyone considering giving CoQ10 to someone under 18 — supplements like this are formulated for adults
None of this is unusual, by the way — it's the same checklist we'd give for most food supplements. It's just that CoQ10's blood-thinner interaction makes the "ask first" rule genuinely important rather than boilerplate.
How to start sensibly
If you've checked the list above and you're going ahead:
- Follow the label. Take the stated serving — don't assume more is better.
- Take it with a meal containing some fat, unless the label says otherwise.
- Earlier in the day if you find it affects your sleep.
- Give it a consistent run rather than chopping and changing products week to week.
- If something feels off, stop and ask — pharmacist or GP.
That's it. Unglamorous, but that's rather the point.
A note on quality — because it's a safety issue too
One under-discussed side-effect risk isn't the ingredient, it's the product: poorly made supplements can contain less active ingredient than stated, or contaminants that shouldn't be there at all. That's a quality problem that no dosage advice can fix. It's why third-party batch testing and GMP manufacturing aren't marketing decoration — they're the checkable difference between a label and a promise.
Frequently asked questions
Is CoQ10 safe to take?
CoQ10 is generally well tolerated at the servings found in supplements. Reported side effects are usually mild — most commonly digestive upset. It can interact with some medicines, including blood thinners, so speak to a pharmacist or GP first if you take any prescription medication.
What are the most common side effects of CoQ10?
The most commonly reported are digestive upset (nausea, stomach discomfort, loose stools), occasional headaches, and trouble sleeping if taken late in the day. Taking it with a meal usually helps.
Can I take CoQ10 with blood thinners like warfarin?
Not without checking first. CoQ10 may reduce how well some blood-thinning medicines work. Speak to your pharmacist, GP or anticoagulation clinic before adding CoQ10 to an anticoagulant.
Does CoQ10 interact with statins?
Statins can lower the body's own CoQ10 levels, which is why the two are often discussed together. Whether supplementing helps is not established, and no UK health claims are authorised. If you take a statin, ask your pharmacist before starting CoQ10.
Can I take CoQ10 while pregnant or breastfeeding?
There isn't enough good data in these groups, so the careful answer is to speak to your GP or midwife before taking it.
What should I do if I get side effects from CoQ10?
Stop taking it and speak to a pharmacist or your GP. Mild digestive upset sometimes settles when taken with food, but anything persistent or concerning is worth a professional's two minutes.
Food supplement. Do not exceed the recommended daily dose. Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. If you are pregnant, breastfeeding, taking medication, or have a medical condition, please consult your doctor before starting.