What to do if medical cannabis makes symptoms worse

If medical cannabis seems to be making your symptoms worse, treat it as a safety question first.

That does not mean the medicine is definitely the cause. Symptoms can worsen because of the original condition, another illness, an interaction with another medicine, a side effect, impairment, anxiety, sleep disruption, or something unrelated. But the practical next step is the same: do not try to solve it through guesswork.

If someone may be seriously unwell, at risk of harm, unable to stay safe, having severe physical symptoms, or showing signs of a life-threatening emergency, use 999 or A&E. If it feels urgent and you are not sure what level of help is needed, use NHS 111. If it is not an emergency but the symptoms are concerning, contact the prescribing clinic, specialist, or medical team that is responsible for the treatment.

MCPH is general UK medical cannabis information only. It is not personal medical advice, diagnosis, prescribing, emergency support, or a substitute for your own clinician, prescriber, pharmacist, NHS 111, 999, or A&E. See the MCPH medical disclaimer and editorial policy for the site boundary.

First, decide whether this is urgent

The first question is not “is this definitely the cannabis?” It is “how unsafe does this feel right now?”

Use emergency help if there is a serious immediate risk. NHS emergency advice says 999 is for life-threatening emergencies. NHS urgent mental health advice also says 999 or A&E is needed if someone’s life is at risk, or if they cannot keep themselves or someone else safe.

That boundary matters with medical cannabis because some possible side effects are not just mild inconvenience. NHS medical cannabis guidance lists possible effects such as dizziness, feeling very tired, mood or behaviour change, feeling high, hallucinations, and suicidal thoughts. If the worrying change is severe, sudden, dangerous, or linked to self-harm risk, it should not wait for a routine clinic message.

Use NHS 111 if you need help now but are not sure where to go. NHS 111 can assess symptoms and direct you to the right place, including urgent treatment, specialist support, 999, A&E, pharmacy help, or another route.

What “making symptoms worse” can mean

People often use “worse” to mean several different things. It helps to separate them before speaking to a clinician.

It may mean the original condition feels worse. Pain may feel harder to manage. Nausea may be more intrusive. Sleep may be disrupted. Anxiety, mood, or intrusive thoughts may become more difficult. Spasticity, headaches, fatigue, or other symptoms may feel different from the usual pattern.

It may mean a new side effect has appeared. NHS lists possible medical cannabis side effects including nausea, diarrhoea, appetite changes, weakness, dizziness, tiredness, feeling high, hallucinations, mood or behaviour change, and suicidal thoughts. Not everyone gets these, and the pattern will depend on the person and the prescribed medicine, but they are the kind of symptoms worth taking seriously.

It may mean another medicine is involved. NHS says CBD and THC can affect how other medicines work, and possible interactions should be discussed with a specialist. That is one reason this should go back to the prescribing team rather than becoming a home experiment.

It may also mean the problem is not caused by medical cannabis at all. That still needs proper judgement. A prescriber or medical team can look at timing, other medicines, the original condition, physical health, mental health, and any red flags.

What to tell the prescriber or medical team

For non-emergency concerns, contact the prescribing clinic, specialist, or medical team and give them the practical facts. Keep it plain:

• what changed;
• when it changed;
• how severe it feels;
• whether there are mood, behaviour, hallucination, panic, suicidal-thought, fainting, breathing, chest-pain, seizure, confusion, or injury concerns;
• what other prescribed, over-the-counter, or supplement medicines are involved;
• whether alcohol, non-prescribed cannabis, or other substances are involved;
• whether driving, work, caring responsibilities, or machinery could be affected;
• whether you have already contacted 111, 999, A&E, a pharmacist, or another clinician.

This is not about building a perfect report. It is about giving the clinician enough context to decide what needs to happen next.

If you have the medicine packaging, dispensing label, prescription copy, patient information leaflet, or written clinic instructions, keep them available when asking for help. NHS 999 advice also says collecting medicines can help ambulance crews understand what someone is taking, if this can be done without delaying help.

Do not turn it into a product or dose experiment

This is the bit where patient forums and comment sections can become risky. A symptom getting worse is not a good moment to compare strains, products, routes, or personal routines with strangers online.

Medical cannabis can be prescribed in different forms and under different clinical circumstances, but suitability, monitoring, interactions, impairment, and risk factors sit with the prescriber. Public advice cannot safely tell one patient what to alter because another patient had a different experience.

The safer version is boring, but it is the right one: use urgent services when the situation is urgent, and use the prescribing team for treatment-specific advice. If there is a patient information leaflet or written clinic safety instruction, use that as the supplied medicine information and escalate if symptoms are worrying.

If mood, anxiety, hallucinations, or suicidal thoughts are involved

Mental health changes deserve a lower threshold for help.

NHS medical cannabis guidance lists mood or behaviour change, hallucinations, and suicidal thoughts among possible side effects. That does not prove medical cannabis is the cause in any individual case. It does mean those symptoms should not be brushed off as ordinary discomfort.

Use NHS 111 for urgent mental health help when immediate expert advice is needed and the situation is not already a life-threatening emergency. Use 999 or A&E if someone’s life is at risk, they have seriously injured themselves, they have taken an overdose, or they cannot keep themselves or someone else safe.

If you are supporting someone else, stay with the practical facts. What changed? When? Are they safe right now? What have they taken, prescribed or otherwise? What support is already involved? If there is immediate risk, do not wait for a clinic inbox.

Reporting side effects through Yellow Card

If you suspect a side effect from medical cannabis, you can report it through the MHRA Yellow Card scheme. NHS medical cannabis guidance points patients to Yellow Card as well as telling them to report side effects to their medical team. NICE and GMC also point adverse-event reporting towards Yellow Card.

Yellow Card matters because it helps the medicines regulator spot safety signals. It is not personal medical advice. The MHRA Yellow Card site says it cannot provide medical advice and directs people who are worried about their health to a doctor, pharmacist, or NHS 111.

The practical order is simple: urgent help first if needed, prescriber or medical team for personal advice, Yellow Card for reporting a suspected side effect.

Driving, work, and safety-critical tasks

If medical cannabis, a side effect, or worsening symptoms could affect alertness, judgement, coordination, mood, or perception, driving and safety-critical tasks need caution.

GOV.UK drug-driving guidance says it is illegal to drive if legal or illegal drugs make someone unfit to drive. Prescription medicines are legal drugs in this context. GOV.UK also says people taking prescription or over-the-counter medicines should speak to a doctor, pharmacist, or healthcare professional if unsure about driving.

A prescription is not a blanket answer to impairment. This guide cannot tell you when you are fit to drive, work with machinery, care for someone safely, or do a safety-critical job. If that question is live, raise it with a healthcare professional and err away from risk while you are seeking advice.

What a clinician may need to work out

A prescriber or medical team may need to decide whether the symptoms look like:

• a side effect;
• an interaction with another medicine;
• the original condition worsening;
• a mental health concern;
• impairment or sedation;
• a separate illness;
• a product-quality or supply issue;
• something that needs urgent assessment.

That is why the article cannot reduce this to “normal side effect” or “wrong product”. Some effects may be manageable with clinician guidance. Others may need urgent care. Some may turn out not to be related to medical cannabis at all.

The useful thing for a patient or carer is to notice the change, take the severity seriously, and get the right level of help.

Bottom line

If medical cannabis seems to make symptoms worse, do not try to solve it by guessing.

Use 999 or A&E for life-threatening emergencies or immediate safety risks. Use NHS 111 when you need medical help now and are not sure where to go. For non-emergency but concerning symptoms, contact the prescribing clinic, specialist, or medical team. Use Yellow Card to report suspected side effects, but not instead of getting medical advice.

MCPH can help with general education through the articles section, but urgent symptoms and treatment decisions belong with NHS urgent care routes and the clinicians responsible for the prescription.

Sources

• NHS: Medical cannabis – https://www.nhs.uk/medicines/medical-cannabis/
• NHS: When to use NHS 111 online or call 111 – https://www.nhs.uk/nhs-services/urgent-and-emergency-care-services/when-to-use-111/
• NHS: When to call 999 – https://www.nhs.uk/nhs-services/urgent-and-emergency-care-services/when-to-call-999/
• NHS: Where to get urgent help for mental health – https://www.nhs.uk/nhs-services/mental-health-services/where-to-get-urgent-help-for-mental-health/
• MHRA Yellow Card – https://yellowcard.mhra.gov.uk/
• NICE NG144: Cannabis-based medicinal products – https://www.nice.org.uk/guidance/ng144
• GMC: Information for doctors on cannabis-based products for medicinal use – https://www.gmc-uk.org/professional-standards/learning-materials/information-for-doctors-on-cannabis-based-products-for-medicinal-use
• CQC: Cannabis-based medicinal products, what CQC expects from providers – https://www.cqc.org.uk/guidance-providers/healthcare/cannabis-based-medicinal-products-what-cqc-expects-providers
• NHS England: Cannabis-based products for medicinal use – https://www.england.nhs.uk/long-read/cannabis-based-products-for-medicinal-use-cbpms/
• GOV.UK: Drugs and driving, the law – https://www.gov.uk/drug-driving-law