Not in the labels, but close to one warning
A search of the US prescribing information, the EU summary of product characteristics and the Canadian monograph finds no entry for brain fog, cognitive impairment, memory or concentration as a reaction to Victoza®, and none of the Canadian trial tables, which list every event above 1%, includes one. [1][2][3] What all three do describe, in overlapping words, is low blood sugar.
| Source | Where it appears | Wording (paraphrased) |
|---|---|---|
| US Medication Guide [1] | Signs of low blood sugar | Confusion or drowsiness, blurred vision, slurred speech, weakness, dizziness |
| EU package leaflet [2] | Signs of low blood sugar; driving | Feeling confused, sleepy or weak, difficulty concentrating; low blood sugar may reduce your ability to concentrate |
| Canadian patient information [3] | Signs of low blood sugar; driving | Feeling sleepy, confused, difficulty concentrating; avoid low blood sugar while driving |
| All three, adverse reaction lists [1][2][3] | Side-effect tables | No brain fog, memory or concentration entry |
Low blood sugar: the label’s route to a foggy head
The US label warns that adults using Victoza® with a sulfonylurea or insulin may have more low blood sugar, including severe episodes, and that in patients aged 10 and older the risk was higher with Victoza® whatever else they took. [1] In the paediatric trial, 21.2% of young people had at least one reading below 54 mg/dL. [1] MedlinePlus explains that unclear thinking tends to appear when blood sugar falls further, below 54 mg/dL, and that some people do not notice the early warning signs at all. [10]
The European label rates Victoza®’s own effect on driving as none or negligible, but asks people to guard against low blood sugar at the wheel, particularly with a sulfonylurea or insulin. [2]
High blood sugar matters too
The GRADE trial randomised 3,721 adults with type 2 diabetes of under ten years, already on metformin, to add insulin glargine, glimepiride, liraglutide or sitagliptin, and followed them for about four years. [4] Cognitive scores did not differ between the four medicine groups. [4] What did matter was blood sugar: each one-point rise in average HbA1c was linked to slightly lower scores on tests of processing speed, word recall and verbal fluency. [4] MedlinePlus lists feeling weak or tired and blurred vision among symptoms of high blood sugar. [11] In other words, poorly controlled diabetes can itself cloud thinking, which is one of the things Victoza® is prescribed to address.
Other liraglutide studies of thinking
Two smaller trials looked for benefit rather than harm. In an Italian study of 40 adults with obesity and prediabetes or new type 2 diabetes, people given liraglutide 1.8 mg a day until they had lost about 7% of their weight showed better short-term memory scores than those who reached the same weight loss with lifestyle changes. [5] Only 16 per group completed the testing, so the result is tentative. [5] In the ELAD trial, 204 people with mild to moderate Alzheimer’s disease and no diabetes took daily liraglutide or placebo for a year; brain glucose metabolism, the main outcome, did not differ, one executive-function score was better on liraglutide, and the treatment was generally well tolerated. [6]
None of these trials was designed to detect brain fog as a side effect, and none reported it as one. [4][5][6] On the other side, an analysis of US spontaneous reports across six GLP-1 medicines, including liraglutide, found nervous system signals such as lethargy and hypoglycaemic unconsciousness; such reports cannot give rates or show cause. [7]
Other causes of a foggy head
Cleveland Clinic describes brain fog as a cluster of symptoms: difficulty concentrating, forgetfulness, slow thinking, mental exhaustion and losing words. [8] Its list of common causes includes poor sleep, diabetes and low blood sugar, anxiety and depression, hormonal changes such as menopause, poor nutrition, stress, infections including COVID-19, and some medicines. [8]
MedlinePlus, writing about confusion, adds fever, infection, fluid or electrolyte imbalance, alcohol, lack of sleep, low oxygen and deficiencies of niacin, thiamine or vitamin B12, and notes that confusion is more common in older people. [9] For someone with type 2 diabetes, several of these can overlap at once.
Steps the sources describe
Cleveland Clinic notes there is no specific treatment for brain fog and lists better sleep habits, nutritious meals, daily physical activity, writing important things down and short breaks during the day. [8] It suggests talking to a provider when fog interferes with daily life. [8]
For confusion that comes on suddenly because of low blood sugar from a diabetes medicine, MedlinePlus says the person should take a sweet drink or snack and that their provider should be contacted if the confusion lasts longer than ten minutes. [9] Before the first dose, the Victoza® Medication Guide asks for a conversation with your provider about low blood sugar and what to do when it happens. [1]
Victoza® is a registered trademark of Novo Nordisk A/S. PepLabo is not affiliated with or endorsed by Novo Nordisk A/S.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Sudden confusion in someone with diabetes, or confusion with clammy skin, a fast pulse, fever or loss of consciousness | Emergency services (911 or local number) | Emergency | MedlinePlus [9] |
| Confusion that does not lift after a sweet drink or snack within about ten minutes | Contact the provider; call emergency services if the person becomes less alert | Emergency | MedlinePlus [9][10] |
| Foggy thinking with shakiness, sweating, hunger or blurred vision, especially on insulin or a sulfonylurea | Check and treat per your low blood sugar plan; tell your prescriber | Today | Medication Guide [1] |
| Foggy thinking with ongoing vomiting or diarrhea, or passing very little urine | Your prescriber, the same day | Today | Medication Guide [1]; MedlinePlus [9] |
| Thirst, blurred vision, tiredness and passing more urine than usual | Discuss your blood sugar control with your provider | At your next appointment | MedlinePlus [11] |
| Brain fog that disrupts work, appointments or conversations | Book an appointment | At your next appointment | Cleveland Clinic [8] |
