CBD Guides

CBD side effects: what UK consumers need to know

By the Honest CBD Co team · 23rd July 2026 · Updated 20th August 2026

What are the side effects of CBD?

For most people, CBD side effects are mild, and the most commonly reported ones settle down once the dose is adjusted or stopped. Even so, it’s worth knowing what to expect before you start, particularly if you’re new to cannabidiol or taking other medicines.

The most frequently reported adverse effects across clinical studies include:

Drowsiness and somnolence: feeling sleepy or sluggish, particularly at higher doses
Dry mouth: less saliva than usual, which can feel uncomfortable
Diarrhoea and gastrointestinal discomfort: loose stools or an upset stomach, especially when starting out
Decreased appetite: some people notice they feel less hungry
Fatigue: a general sense of low energy, distinct from drowsiness
Dizziness: occasional lightheadedness, usually at higher doses
Mood changes: mild shifts in mood or irritability in some people

These CBD adverse effects are generally mild to moderate and tend to ease when you lower the dose or stop taking it. How severe they are depends on a few things: how much you take, the form of CBD you use, and the purity of the product itself.

Product type matters more than many people realise. Full spectrum CBD contains trace levels of THC and other cannabinoids alongside CBD, whereas CBD isolate is refined to 98% or above pure cannabidiol. That difference in composition can influence how your body responds, which is why product purity matters so much when you’re choosing a supplement.

Common CBD side effects explained in more detail
Safety considerations and risks of CBD use in the UK
How CBD can interact with your medications
CBD and medical cannabis: understanding the legal difference in the UK
How to minimise side effects through sensible CBD dosing
About Honest CBD Co
Key takeaways

Common CBD side effects explained in more detail

Understanding why these symptoms happen helps you manage them with a bit more confidence. Most arise because CBD interacts with receptors throughout the body, including those involved in digestion, sleep regulation and the central nervous system.

Drowsiness and fatigue

Somnolence is one of the most consistently documented effects in human studies and tends to appear at relatively higher doses, though some people notice mild tiredness at lower amounts. If you take CBD in the evening, this can actually be a welcome effect. Taken in the morning, it may get in the way of concentration. Starting low and adjusting gradually is the most practical way to find a dose that works without leaving you feeling foggy.

Gastrointestinal symptoms

Diarrhoea, nausea and abdominal discomfort are among the more common complaints, particularly when you first start taking CBD or take it on an empty stomach. These symptoms usually ease within a few days as your body adjusts. Taking CBD oil with food tends to reduce stomach irritation noticeably.

Appetite changes

Decreased appetite shows up in clinical trial data fairly consistently. Unlike THC, which is well known for increasing hunger, CBD can have the opposite effect in some people. For most healthy adults this isn’t a concern, but it’s worth keeping an eye on if you already have a reduced appetite or are managing a condition affected by nutrition.

Less common effects

Dizziness: more likely when standing up quickly after taking CBD, possibly linked to a temporary drop in blood pressure
Mood changes: mild irritability or low mood in a small number of users; not well understood, but documented in some reports
Rash or hypersensitivity: rare, but possible; stop taking it and seek advice if a skin reaction develops
Sleep disturbance: oddly, some people report poorer sleep at higher doses despite CBD’s sedative reputation at lower ones

Does the form of CBD change the side effects?

To a degree, yes. CBD oils taken sublingually (under the tongue) act faster and tend to produce more pronounced short-term effects because absorption is more direct. Capsules pass through the digestive system first, which slows onset but can increase gastrointestinal symptoms in sensitive individuals. Topical CBD products, such as a body salve applied to the skin, are absorbed locally and are very unlikely to cause systemic side effects like drowsiness or appetite changes. They’re generally considered the lowest-risk format for people who are cautious about taking CBD internally.

Safety considerations and risks of CBD use in the UK

CBD isn’t risk-free, and it’s worth knowing what UK regulators say. The Food Standards Agency (FSA) advises healthy adults to keep CBD intake from food supplements to about 10mg a day. That advice is deliberately precautionary; it is not a legal limit and it is not a maximum dose.

Some honest context: the FSA’s own guidance was 70mg a day until autumn 2023, and clinical research has used doses in the hundreds of milligrams. In our experience since 2018, many regular users settle between 25mg and 100mg or more a day. We think the current figure is out of step with real-world use, though that’s our opinion, and the official advice is as stated above.

Liver enzyme effects

This is the area of most active concern in recent research. A clinical trial found that 5.6% of healthy adults taking CBD at approximately 5 mg/kg/day for 28 days experienced elevated liver enzymes (ALT or AST more than three times the upper limit of normal), with no clinical symptoms observed during the study. That finding matters: liver stress can occur without you feeling unwell. Liver enzyme elevations linked to CBD often go unnoticed, which is why professional advice and monitoring matter, especially for long-term or high-dose users.

Signs of adverse effects on the liver have been observed at certain higher doses in patients and healthy volunteers, and the FSA notes that humans may be more sensitive to CBD’s liver effects than laboratory animals.

Vulnerable groups: who should avoid CBD?

The FSA and NHS are explicit about which groups should not use CBD food supplements:

Pregnant and breastfeeding women: gaps in the safety data mean the risk can’t be properly assessed
Children: advised against consumption due to residual uncertainties
People trying to conceive: prospective parents are advised to avoid CBD
Immunosuppressed individuals: not enough data to confirm safety in this group

The FSA’s advice is consistent: if you fall into any of these categories, avoid CBD food products or speak to your GP before considering use.

Product purity and contaminants

Full spectrum products contain minor cannabinoids and, in some cases, trace THC. Those extra compounds change the toxicity profile compared with pure CBD isolate, which is why product purity matters. Unregulated or poorly made supplements may contain impurities that raise the risk of side effects considerably, so buy from a seller who can tell you exactly what’s in their products and how much THC they contain.

How CBD can interact with your medications

CBD’s interaction with prescription drugs is one of the most clinically significant concerns for UK consumers, and one that doesn’t always get enough attention on product labels or in general wellness content.

The core mechanism is straightforward: CBD inhibits a group of liver enzymes called cytochrome P450, specifically CYP3A4 and CYP2C19. These enzymes metabolise a large proportion of commonly prescribed medicines. When CBD slows their activity, drug concentrations in the blood can rise or fall unpredictably, altering both effectiveness and the risk of side effects.

Which medications are most affected?

Anticoagulants (e.g., warfarin): CBD can increase blood levels, raising bleeding risk
Antiepileptic drugs (e.g., clobazam, valproate): interactions are well documented; valproate combined with CBD specifically increases the risk of liver enzyme elevations
Immunosuppressants (e.g., tacrolimus, ciclosporin): narrow therapeutic windows make any interaction potentially serious
Certain antidepressants and antipsychotics: metabolised via CYP2D6 and CYP3A4 pathways
Sedatives and hypnotics: additive sedation is possible when combined with CBD
Some statins and calcium channel blockers: metabolised via CYP3A4

Clinical experts recommend that anyone on regular medication talks to their GP before using CBD, to avoid adverse drug interactions. This isn’t a box-ticking precaution; it reflects genuine clinical risk.

What the NHS says

NHS guidance is clear that CBD can affect how other medicines work in your body. If you’re taking any prescription drug, the responsible step is to tell your healthcare provider before adding CBD to your routine. The MHRA (Medicines and Healthcare products Regulatory Agency) also monitors CBD-related safety signals in the UK, and any serious adverse reactions to CBD products can be reported through the Yellow Card scheme.

Inhibitory drug-drug interactions have been observed with some medications when CBD is co-administered at doses of 1 mg/kg body weight per day, equivalent to 70 mg in a 70 kg adult. How likely interactions are at lower doses hasn’t been fully worked out, which means caution is sensible even at the amounts found in typical food supplements.

CBD and medical cannabis: understanding the legal difference in the UK

These two terms are often used interchangeably, but they describe very different products under UK law, with different regulatory standards, safety monitoring and intended uses.

CBD as a food supplement

CBD sold as a food supplement in the UK is regulated as a novel food by the FSA. It isn’t a medicine, has no formal medical approval, and can’t legally be marketed with claims that it treats or prevents any health condition. Products must comply with novel food authorisation requirements, including compositional standards and labelling rules. THC content in CBD products must stay within legal limits; any product containing THC above those limits is illegal to sell.

Medical cannabis

Medical cannabis is an entirely separate category. Since November 2018, cannabis-based products for medicinal use can be prescribed in England, Wales and Scotland when there’s an unmet clinical need. These products are classified as Schedule 2 controlled drugs under the Misuse of Drugs Regulations 2001 and can only be prescribed by specialists listed on the GMC’s specialist register. The NHS is explicit that consumers shouldn’t expect CBD food supplements to deliver the same outcomes as prescribed medical cannabis, which is strictly monitored for adverse effects.

Key distinctions at a glance:

CBD supplements: sold legally as food products, not medicines; no prescription required; regulated by the FSA
Medical cannabis: prescription only; strictly controlled; monitored for efficacy and adverse effects; prescribed for serious conditions such as treatment-resistant epilepsy, chemotherapy-induced nausea and MS-related spasticity
THC limits: CBD food products must contain no more than 1 mg of THC per container; products exceeding this are controlled substances
Driving: THC is detectable in the blood and saliva tests used by UK police. Even trace amounts from full spectrum CBD products could in theory trigger a positive roadside test, so be careful if you drive regularly

The regulatory gap between these two categories matters for safety. Medical cannabis is assessed for risk-benefit balance; CBD supplements are assessed only for safety, with no clinical benefit required to justify their use. That means the burden of making an informed decision rests more heavily on you as the consumer.

How to minimise side effects through sensible CBD dosing

Getting the dose right is the single most effective way to reduce the chance of unwanted effects. There’s no universal dose that works for everyone, but there are clear principles that help.

Start low and go slow

The most practical approach is to start low, at around 10-20mg a day, and give it a fair trial before changing anything. That gives your body time to adjust and makes it easier to spot the dose where you feel the benefit without side effects. If nothing much happens after a week or two, step up gradually until you find the level that works for you. Everyone\x{2019}s level is different, and there is no prize for rushing. Our CBD dosage guide walks through the process, and if you are wondering how much is too much, the honest answer is in our guide to CBD overdose: no fatal overdose from pure CBD has ever been recorded.

Practical dosing tips to reduce adverse effects

Take CBD with food: this reduces gastrointestinal side effects and can improve absorption
Avoid taking CBD close to other medications: spacing doses reduces the risk of interaction effects
Don’t combine CBD with alcohol or sedatives without medical advice, as additive sedation is a real risk
Track your dose and symptoms: a simple log helps you spot patterns and adjust accordingly
Use one product at a time: stacking several CBD formats makes it harder to keep track of your total daily intake

One sensible caveat: build up gradually, and talk to your GP or pharmacist before starting if you take prescription medication or are pregnant or breastfeeding. If you notice any persistent or unusual symptoms after starting CBD, reduce the dose or stop.

About Honest CBD Co

If you’ve read this far, you already know that product quality isn’t a minor detail when it comes to CBD safety. It determines your actual dose and your exposure to contaminants.

We’re Honest CBD Co, a husband-and-wife business based in Bolton. We’ve been making CBD products here in the UK, in small batches, since 2018, and we’re rated Excellent on Trustpilot with 732 reviews. Our approach is simple: plain products, honest prices, no hype.

If you want a straightforward starting point, our Full Spectrum CBD Oil comes in 10ml bottles at 10% (1000mg) or 20% (2000mg), so you can start low and adjust your dose drop by drop without switching products. If you’d rather avoid THC altogether, our Pure CBD Isolate Oil is flavourless and THC-free. For measured, consistent dosing there are Full Spectrum CBD Capsules in three strengths: 40mg for starting out, 80mg for regular users, and 120mg for experienced users who know their level. And if you’d prefer not to take CBD internally at all, our CBD Body Salve is THC-free and for external use only. Whatever you choose, browse the full range and pick the format that suits you.

Key takeaways

CBD side effects are real but manageable. Starting low, stepping up gradually, and buying from a reputable UK seller who’s upfront about what’s in the bottle significantly reduces your risk.

Point	Details
Most side effects are mild	Drowsiness, dry mouth, diarrhoea and appetite changes are the most common; they usually resolve with dose adjustment.
Liver enzyme risk is real	A 2025 clinical trial found 5.6% of healthy adults taking CBD at approximately 5 mg/kg/day for 28 days experienced elevated liver enzymes, with no outward symptoms.
Start low and build up	Begin at around 10-20mg a day, give each dose a fair trial, and step up gradually until you find the level that works for you. The FSA’s precautionary food-supplement advice is not a legal limit.
Medication users must consult a GP	CBD inhibits CYP3A4 and CYP2C19 enzymes, potentially altering blood levels of anticoagulants, antiepileptics and other drugs.
Buy from a seller you can trust	We’ve made small-batch CBD in the UK since 2018 as a family business, with honest pricing and an Excellent Trustpilot rating from 732 reviews.