What is it?
Cannabis comes from the cannabis plant and contains many compounds, including THC (associated with the 'high') and CBD. Strength varies widely and is often unknown. Synthetic cannabinoids are different chemicals and carry distinct, often greater, risks.
Common forms
- Herbal cannabis
- Resin
- Concentrates and oils
- Edibles
- Vapes
How it affects the body
Cannabinoids act on receptors in the brain that influence mood, memory, appetite, coordination and perception of time.
Short-term effects
- Relaxation or talkativeness
- Altered perception
- Increased heart rate
- Anxiety or panic in some people
- Impaired coordination, memory and driving ability
Long-term effects
- Respiratory problems when smoked, especially with tobacco
- Effects on motivation, memory and learning
- Increased risk of psychosis for some people, particularly with strong products, frequent use or a family history
- Dependence in some regular users
Dependence and addiction
Dependence can develop when the body and brain adapt to regular use. It is not a moral failing or a lack of willpower. Signs people describe include needing more to get the same effect, difficulty cutting down, spending more time thinking about use, and continuing despite harm. Support is available at any stage — you do not need to have reached a crisis point.
Withdrawal
Stopping or reducing after regular use can cause withdrawal. Withdrawal varies between people and depends on how much and how long someone has used, their physical health and other substances involved. Some withdrawal can be medically serious, so it is safer to plan a reduction with a clinician or a drug and alcohol service rather than stopping abruptly alone. People commonly describe sleep problems, irritability, low mood, restlessness and reduced appetite.
Overdose risks
Fatal overdose from cannabis alone is not typical, but people can become acutely unwell — particularly with edibles, where effects are delayed and easy to over-consume, and with synthetic cannabinoids. Seek urgent help for severe agitation, chest pain, persistent vomiting or unresponsiveness.
Mixing substances
Mixing with alcohol or other sedating substances increases impairment. Smoking with tobacco adds nicotine dependence and respiratory harm.
Harm-reduction information
- Avoid driving or operating machinery
- With edibles, effects are delayed — waiting rather than re-dosing reduces risk
- Avoid synthetic cannabinoids; effects are unpredictable
- If you have a personal or family history of psychosis, the risks are higher
- Talk to a service if use is affecting your mood, sleep, study or work
When to seek urgent medical help
Call 999 if someone is unconscious or cannot be woken, is having difficulty breathing, has a seizure, has chest pain, becomes very confused or agitated, or you are worried they may have overdosed. For urgent advice that is not life-threatening, call NHS 111. You will not get someone into trouble by calling for medical help.
Treatment and recovery options
- Talking therapies and structured psychosocial support
- Community drug and alcohol services, including self-referral where available
- Medication-assisted treatment where clinically appropriate
- Medically supported withdrawal, arranged and monitored by clinicians
- Peer support and recovery communities
- Residential rehabilitation for some people, usually via assessment
- Support for related needs — mental health, housing, family and welfare
UK support resources
- NHS — health information and service finders (nhs.uk)
- Talk to FRANK — UK drug information service (talktofrank.com)
- Your local community drug and alcohol service — many accept self-referrals
- Local pharmacy teams, who can offer advice and signposting
Sources / references
This page is a plain-language summary written for education. For clinical or legal detail, use authoritative UK sources: NHS (nhs.uk), Talk to FRANK (talktofrank.com), NICE (nice.org.uk), UK Government and devolved government publications, and guidance from UK professional bodies. Each page on this site carries a review date, and we welcome corrections.