Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

What is seasonal affective disorder?

Seasonal affective disorder (SAD) is a temporary, repetitive form of depression triggered by yearly seasonal patterns. 

For most people, the onset of SAD is in autumn. Symptoms continue for around four to five months and then resolve in the spring.

A small number of people with SAD experience the opposite seasonal pattern. Their symptoms begin in spring and continue throughout the summer before ending in autumn. 

SAD isn’t the same as having the ‘winter blues’ (also known as ‘subsyndromal SAD’). Although some of the symptoms appear similar, SAD is more severe. SAD negatively impacts your everyday life, can be debilitating, and prevents you from living your life to the fullest. 

Living with SAD, however, doesn’t have to be this way. By recognizing the symptoms and the early signs of SAD, you can get on top of it and learn effective ways to better manage or even alleviate your symptoms.

Who’s at risk of seasonal affective disorder?

According to the American Psychiatric Association, SAD impacts approximately 5% of all adults in the United States¹. 

 Anyone can get SAD, but some people are more prone to it. These include:

  • Women, who are four times² more likely than men to be diagnosed with SAD

  • Young adults between the ages of 18 and 30¹

  • People who live a long distance from the equator, especially those in the far north (for winter-pattern SAD). It’s also thought that among these people, the symptoms of SAD are more severe and tend to last longer².

  • People who have a family history of SAD

  • People with other mental health conditions, such as bipolar disorder or major depressive disorder

  • People with low vitamin D levels³, common among people living in areas with less sunlight. Vitamin D enhances the production and release of serotonin, a chemical messenger in the brain that regulates mood. 

What causes the symptoms of seasonal affective disorder?

Although the exact causes of SAD are unknown, experts believe that a range of factors contributes to its symptoms. These link back to either reduced exposure to sunlight (in autumn-onset SAD) or excessive exposure (in spring-onset SAD).


Low serotonin levels are linked to various mental health conditions, including SAD. 

Serotonin is a chemical messenger (hormone) that the body produces (90% is made in the gut) and is used by the brain to regulate mood. Its function is to send messages between nerve cells. 

Some experts believe that the amount of serotonin in the brain differs from season to season. During winter, it’s thought that more serotonin is reabsorbed into the nerve cells that produced it, preventing it from sending messages to other cells. 

Low sunlight (or vitamin D levels) in the winter plays a role in lower serotonin levels since vitamin D triggers serotonin production in the body. As a result, mood and behavior regulation are negatively impacted by this imbalance.

Thus, this could be a link to SAD. 

The circadian rhythm

The circadian rhythm is the ‘biological clock’ in our body that controls many processes. 

Experts believe that during the transition from summer to autumn and winter, some people’s biological clock can get disrupted as the hours of sunlight each day decrease. It becomes out of sync with their sleep-wake cycle and the day-night cycle of the season. 

This is thought to lead to depression-related symptoms and subsequent changes to sleep, mood, and behavior. 


Melatonin is a hormone produced by the brain in response to darkness. The brain generally begins producing this hormone an hour or two before you go to bed. 

Melatonin is important in the sleep-wake cycle as it makes people feel tired and is associated with the circadian rhythm.

A change in seasons can disrupt melatonin production. During winter, the days shorten, so there are fewer hours of sunlight and more hours of darkness. 

This means many people have increased melatonin levels during the winter, possibly explaining why people with winter SAD experience excessive sleep and fatigue. 

What are the symptoms of seasonal affective disorder?

The symptoms of SAD, and the impact that it has on life, vary between people. While some people experience SAD mildly, it can be severe for others. 

According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), SAD isn’t a separate mental health condition. Instead, it’s categorized as a subtype of major depressive disorder.

Many symptoms of SAD are shared with the more generalized non-seasonal major depressive disorder. Some of these symptoms may include:

  • Feeling sad throughout the day, on most days 

  • Losing interest in hobbies and everyday activities that you normally enjoy 

  • Feeling hopeless or guilty 

  • Changes in appetite or weight

  • Changes in sleep patterns

  • Having difficulty concentrating or making decisions

  • Thinking about suicide or hurting yourself. This should be taken extremely seriously, and you should seek immediate medical attention if you have these thoughts. 

Due to these similarities, you may find it difficult to determine whether you’re struggling with general non-seasonal depression or SAD. 

The most significant difference is that the symptoms of SAD usually resolve in the opposite season, but non-seasonal depression does not display a seasonal pattern. 

It’s thought that around 40% of people⁴ diagnosed with SAD continue to experience depression-related symptoms after the season ends, which then prompts the doctor to reconsider their diagnosis.

What differentiates it from non-seasonal depression?

Four characteristics of SAD can help differentiate it from non-seasonal depression:

  • The symptoms and depressive episodes must begin and end at the same time each year

  • These symptoms and depressive episodes must not be experienced during any other seasons in the year

  • Over a lifetime, more seasons with depressive symptoms are experienced than without them

  • The seasonal depressive episodes and the same pattern of symptoms must occur for at least two years in a row

Summer and winter seasonal affective disorder: How the symptoms differ

In some ways, summer (spring-onset) SAD and winter (autumn-onset) SAD are similar. Both affect many of the same bodily functions, such as:

  • Sleep

  • Appetite

  • Weight

  • Relationships

  • Mood

  • Energy levels

However, the specific effect on these bodily functions differs between summer SAD and winter SAD.


People with autumn-onset SAD often experience oversleeping and may have difficulty waking in the morning. Those with spring-onset SAD often have trouble falling or staying asleep (insomnia).

Appetite changes

In autumn-onset SAD, people can experience a greater appetite, and they often report having more cravings for carbohydrates, like sugary or starchy foods. 

Conversely, people with spring-onset SAD often have a lower appetite than normal.

Weight changes

People with autumn-onset SAD can experience unintentional weight gain, most likely due to the increase in appetite. Those with spring-onset SAD experience unintentional weight loss, most likely due to a loss of appetite. 

Mood and energy levels

People with autumn-onset SAD often feel more tired than usual and have low energy levels throughout the day despite sleeping more. Those with spring-onset SAD also experience low moods. However, rather than feeling lethargic, it’s more common for them to feel irritable, agitated, or anxious. 


People with autumn-onset SAD often withdraw from people and have fewer social connections. Some people also experience rejection sensitivity². Those with spring-onset SAD might display agitated or violent behavior toward others. 

Other physical symptoms

Some people with autumn-onset SAD experience leaden paralysis², which is a heavy feeling in the arms and legs that makes you feel weighed down. 

How do the symptoms play out through the season?

In both spring-onset and autumn-onset SAD, it’s not uncommon for symptoms to be mild at the beginning of the season. 

However, without prompt diagnosis and treatment, these symptoms can significantly worsen without quick diagnosis and treatment throughout the season. Several complications can arise, which could include: 

  • Having problems at school or work

  • Developing other mental health disorders, like anxiety 

  • Developing substance abuse

  • Having suicidal thoughts or behavior

Although it may not be curable, you can effectively manage the symptoms of SAD with treatment. The specific treatment recommended to you partly depends on whether you have spring-onset or autumn-onset SAD or other health conditions. 

Some treatments include:

Some experts recommend re-implementing this treatment regime the following year as a preventative measure in preparation for the repetition of SAD-related symptoms. 

What are the signs that a loved one could be living with seasonal affective disorder?

Since SAD is a mental condition, it can be difficult to know when someone is living with it if they don’t open up about their feelings. You might not recognize the inner mental health symptoms they’re struggling with. 

A loved one spending more time alone or acting withdrawn, being extremely irritable, or just acting differently compared to other times of the year could be among the first key signs. 

Spotting the signs of SAD can also be difficult in children, especially those at an age when they can’t accurately describe their symptoms or feelings. 

Although SAD is rare in people under the age of 20⁵, some particular signs to look out for in children include fatigue, irritability, having trouble concentrating, and academic problems at school.

How do you know if you have seasonal affective disorder?

Although no single diagnostic test for SAD exists, the Seasonal Pattern Assessment Questionnaire (SPAQ) is a screening tool used by some doctors and mental health professionals. 

The SPAQ is based on the most common signs and symptoms of SAD. It asks several questions relating to:

  • Any changes in sleep length, social activity, mood, weight, appetite, and energy levels after the seasons change

  • The months when you feel the best and worst, gain and lose the most weight, socialize the most and least, sleep the most and least, and eat the most and least. 

  • How much your weight fluctuates over a given year

  • How many hours of sleep you get per day in each of the four seasons

  • Whether you notice a change in food preferences during different seasons 

  • Whether any changes you experience are mild, moderate, marked, severe, or disabling 

You can use the SPAQ on your own to gauge whether you may have SAD. However, it should never be used as a self-diagnostic tool. It’s best to use it under the guidance of researchers or a medical professional with knowledge and experience in diagnosing and treating SAD. 

When should you see a doctor for seasonal affective disorder?

If you’re experiencing symptoms that you think could be related to SAD, such as feeling low energy and sad during the winter season, don’t hold back from seeing a medical professional, such as your doctor, a psychologist, or psychiatrist.

Your doctor will run tests to rule out the physical causes of your symptoms, such as hypothyroidism

The lowdown

A change in seasons accompanied by changes to your sleep, mood, relationships, weight, appetite, and energy levels could suggest that you are living with SAD. 

It’s important to take all signs and symptoms seriously. With prompt diagnosis and evidence-based treatment, you can manage your symptoms and make SAD easier to live with.

Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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