Education, Medicinal Cannabis in NZ, Travel & Legal Guidance

Winter SAD in New Zealand: Why Lack of Light Affects Your Mood

Posted on by Cannabis Clinic

Frequently Asked Questions

Yes. Medicinal cannabis can be legally prescribed in New Zealand for mental health conditions, including depression and anxiety, when a registered doctor decides it is clinically appropriate,

Winter SAD is a form of depression linked to shorter days and less sunlight. Common signs include low mood, low energy, oversleeping, carbohydrate cravings and difficulty concentrating, appearing on a seasonal pattern that lifts as the days lengthen again. 

It is much less common than winter SAD, but yes. Summer-onset SAD is a recognised condition, usually triggered by heat and humidity rather than light deprivation. Symptoms tend to involve agitation, insomnia, and reduced appetite, which is the opposite pattern to winter SAD. 

Most people begin to see improvement in SAD symptoms within a few days to two weeks of consistent daily use of a 10,000 lux light box. 

Seasonal affective disorder (SAD) is a form of depression that follows the calendar, typically appearing as daylight hours shift or temperatures spike. About 10 per cent of New Zealanders experience some form of seasonal mood change, and many find the transition into the darker months particularly hard to manage.⁴ If you are feeling flat, low on energy or unmotivated now that the days have shortened, you are not alone, and there are things that can help.

SAD is driven by biological shifts in serotonin and melatonin, often described as the “melatonin serotonin seesaw.” Winter pattern SAD is the most common variety in Aotearoa, but summer SAD also exists. Treatment usually involves targeted 10,000 lux light therapy, lifestyle adjustments, and for some people, a doctor may also discuss whether medicinal cannabis could have a role. 

What causes winter SAD? The science of light and mood

The brain relies on environmental light cues to regulate the circadian rhythm, your internal body clock. This system is run by a tiny cluster of cells deep in the brain (suprachiasmatic nucleus) that acts as your body’s master clock.⁵ It reads signals from light sensing cells in your eyes and uses that data to coordinate hormone production.

In bright sunlight, this master clock signals the brain to produce serotonin, which supports a stable mood, focus, and a feeling of calm. As the sun sets, the brain converts serotonin into melatonin, the hormone that prepares you for sleep.⁵

For people living with SAD, this seesaw goes out of balance. Reduced sunlight during a New Zealand winter can cause this clock to overproduce melatonin during the day, leading to drowsiness and low energy. Serotonin levels drop, which can cause low mood, irritability, and intense carbohydrate cravings.⁵

The vitamin D connection

Less light also means less vitamin D. Vitamin D plays a role in regulating serotonin.⁶ In parts of New Zealand with long, overcast winters, particularly in the South Island, vitamin D deficiency can compound the chemical imbalances already taking place in the brain, making seasonal symptoms feel more severe.

How does light therapy help with winter SAD?

Bright light therapy is one of the most effective non-medication treatments for winter SAD.⁸ Household lighting alone is not enough.

Standard home or office lighting provides between 200 and 500 lux. The sun on a clear day can emit upward of 100,000 lux. To trigger the biochemical changes needed to reset circadian timing, you need a much stronger signal.

Clinical guidelines recommend a specialised light box providing 10,000 lux of cool white light.⁸

  • Intensity: 10,000 lux at the recommended distance (usually 40 to 60 cm from the face)
  • Duration: 20 to 30 minutes daily
  • Timing: Within the first hour of waking to advance the circadian clock

Light therapy in the evening is generally not recommended, as it can suppress melatonin at the wrong time and worsen sleep. A device that filters ultraviolet light is also important to protect eyes and skin.⁸

Is your seasonal mood shift affecting your day to day life? Wondering whether medicinal cannabis might be an option for you? Book a consultation.

Is medicinal cannabis legal for SAD in New Zealand?

Yes. Medicinal cannabis has been a formal part of the New Zealand healthcare system since the launch of the Medicinal Cannabis Scheme in April 2020.⁹ While it is not approved specifically for SAD or mood disturbances, doctors can prescribe it for any condition where they believe it will benefit the patient.

These products are treated as unapproved medicines under Section 29 of the Medicines Act 1981. They meet strict quality standards but their use does not have enough evidence to recommend for specific conditions.¹⁰

The legal pathway involves three steps:

  1. Clinical consultation. A doctor or nurse practitioner reviews your medical history, current symptoms, and any potential drug interactions.
  2. Minimum Quality Standard. Your clinician prescribes a product that has been verified by the Medicinal Cannabis Agency to be free from contaminants and consistent in cannabinoid strength.¹¹
  3. Pharmacy dispensing. Your prescription is filled by a registered NZ pharmacy or a specialist clinic dispensary.

Importing medicinal cannabis from overseas for personal use is illegal. The only safe and legal route is through a New Zealand prescriber.

It is also worth noting that higher THC products are not automatically better. For mood and sleep, many NZ clinicians generally favour CBD dominant or balanced formulations rather than high THC products. Any prescribing decision is individualised, and the right formulation, if any, is something a clinician works through with each patient.

How medicinal cannabis may support mood and sleep

Cannabinoids work through the endocannabinoid system, a biological network that helps maintain balance across mood, appetite, and sleep cycles.¹²

In a 2020 New Zealand audit of 400 patients, those prescribed CBD self reported improvements in quality of life, particularly for anxiety and mental distress.¹³ This was a review of everyday practice rather than a controlled trial, and for SAD specifically, large controlled trials are still emerging. Medicinal cannabis is usually considered an option when standard therapies have not provided enough support, rather than a first choice.

Supporting your mood through winter

Beyond clinical treatment, a few practical tools can help.

  • Morning sunlight exposure. Even on an overcast day in Auckland or Wellington, outdoor light is roughly 10 times brighter than indoor lighting. Twenty to thirty minutes outside within two hours of waking helps reset your internal clock.
  • Consistent sleep timing. Keeping the same sleep and wake times, even at weekends, helps stabilise the circadian rhythm. This matters in winter too, when it is tempting to oversleep on dark mornings.
  • Gentle movement. A short daily walk or other light exercise, ideally outside, can genuinely lift mood and energy over the colder months.
  • Staying connected. Winter can make it easier to withdraw from friends and whānau, but staying in touch is one of the simplest ways to protect your mood.
  • Energy mapping. Tracking your energy hour by hour for a week helps identify your slump periods, so you can schedule demanding tasks for higher energy windows and protect lower energy times for rest.
  • Professional oversight. Mood disorders are complex. Having a clinician review side effects, interactions, and treatment changes as the seasons shift is important.

Key takeaways

  • About 10 per cent of New Zealanders experience some form of seasonal mood change.⁴
  • Winter SAD is driven by reduced light and is more common. Summer SAD is more often driven by heat and humidity.
  • 10,000 lux light therapy in the morning is the standard non-medication treatment for winter SAD.
  • Simple habits such as morning sunlight, movement, routine and staying socially connected all help support mood over the darker months.
  • Medicinal cannabis is legal in NZ when prescribed and is usually considered a second line option for mood and sleep symptoms.
  • Higher THC is not automatically better, and any formulation is decided individually with a clinician.

Where to start

If the change of seasons is making it difficult to keep up with work and life, talking to your GP is a good first step, as they can assess what is going on and rule out other causes. If you would like to explore whether medicinal cannabis might have a place in your treatment plan, you can take the Eligibility Quiz or book a consultation to talk it through with one of our doctors. If your mood is consistently low or you are finding it hard to cope, you can also call or text 1737 at any time for free support from a trained counsellor.

References

  1. Ministry of Health NZ. Medicinal Cannabis Scheme: information for consumers. https://www.health.govt.nz/regulation-legislation/medicinal-cannabis/information-for-consumers
  2. Cleveland Clinic. Seasonal depression (SAD). https://my.clevelandclinic.org/health/diseases/9293-seasonal-depression
  3. Mental Health Foundation NZ. Seasonal Affective Disorder (SAD). https://mentalhealth.org.nz/conditions/condition/seasonal-affective-disorder
  4. The Fono. Winter wellness: Seasonal Affective Disorder. https://thefono.org/about-us/news/winter-wellness-seasonal-affective-disorder/
  5. Mayo Clinic. Seasonal affective disorder (SAD): symptoms and causes. https://www.mayoclinic.org/diseases-conditions/seasonal-affective-disorder/symptoms-causes/syc-20364651
  6. Patrick, R. P., & Ames, B. N. (2015). Vitamin D and the omega-3 fatty acids control serotonin synthesis and action. FASEB Journal, 29(6). https://doi.org/10.1096/fj.14-268342
  7. CAMH. Summer depression. https://www.camh.ca/en/camh-news-and-stories/summer-depression
  8. Yale Medicine. Light therapy for winter depression. https://medicine.yale.edu/psychiatry/research/clinics-and-programs/winter-depression/obtain/
  9. Medsafe NZ. Medicinal Cannabis Scheme now operational. https://www.medsafe.govt.nz/profs/PUArticles/June2020/Medicinal-Cannabis-Scheme-now-operational.html
  10. Medsafe NZ. Medicines Information NZ. Using unapproved medicines in New Zealand. https://medicinesinformation.co.nz/using-unapproved-medicines-in-new-zealand/
  11. Ministry of Health NZ. Medicinal cannabis Minimum Quality Standard. https://www.health.govt.nz/regulation-legislation/medicinal-cannabis/information-for-health-professionals/minimum-quality-standard-medicinal-cannabis-products
  12. Hill, M. N., Campolongo, P., Yehuda, R., & Patel, S. (2017). Integrating endocannabinoid signaling and cannabinoids into the biology and treatment of posttraumatic stress disorder. Neuropsychopharmacology, 43(1). https://doi.org/10.1038/npp.2017.162
  13. Gulbransen, G., Xu, W., & Arroll, B. (2020). Cannabidiol prescription in clinical practice: an audit of 400 patients in New Zealand. BJGP Open, 4(1). https://doi.org/10.3399/bjgpopen20X101010

Disclaimer: Medicinal cannabis and CBD oil are unapproved medicines in NZ which means that there is no conclusive evidence for their effect, apart from Sativex. Many doctors do not routinely prescribe cannabis medicines. The above article was written for general educational purposes and does not intend to suggest that medicinal cannabis can be used to treat any health condition. Please consult with your healthcare provider.