What the Trulicity® documents say, and what they leave out
We searched the US label, the EU summary and the Canadian monograph for cognition, memory, concentration and confusion as side effects. None is listed as an adverse reaction of Trulicity®. [1][3][4] Confusion and drowsiness appear only as signs of low blood sugar, and the EU leaflet adds that low blood sugar can reduce your ability to concentrate when driving. [2][3]
The one mention of memory in the US label concerns animal studies: female offspring of rats given dulaglutide in pregnancy, at doses that also reduced the mothers’ food intake, made more errors in a maze test. The label states that the human relevance is not known. [1]
| Effect | Trulicity® | Comparison | Source |
|---|---|---|---|
| Fatigue, asthenia or malaise, 0.75 mg and 1.5 mg | 4.2% and 5.6% | Placebo 2.6% | US Table 1 [1] |
| Fatigue, studies up to 104 weeks | 4.2% and 5.3% | All comparators 4.3% | Canada Table 2 [4] |
| Fatigue, frequency class | Common | — | EU Table 1 [3] |
| Insomnia, 0.75 mg and 1.5 mg | 0.7% and 1.7% | Placebo 1.2% | Canada Table 2 [4] |
| Confusion or drowsiness | Sign of low blood sugar | — | Medication Guide [2] |
What five years of REWIND showed about thinking
REWIND randomised 9,901 adults aged 50 or over with type 2 diabetes to Trulicity® 1.5 mg or placebo and followed them for a median of 5.4 years. [1] An exploratory analysis tested thinking at the start and during follow-up with two standard tools, a brief cognitive assessment and a symbol-matching speed test, in 8,828 participants. [5]
Substantial decline in either test occurred in 4.05 per 100 person-years on dulaglutide and 4.35 on placebo, a difference that was not statistically significant. After a later adjustment for each person’s starting scores, the risk of substantial decline was 14% lower on dulaglutide. [5] The authors called the result a possible benefit needing further study; it was exploratory and funded by the manufacturer. [5] It does not measure day-to-day fogginess, but it offers no sign that long-term dulaglutide harms thinking.
Drug-safety database studies are much less precise: a 2025 analysis found a reporting signal for lethargy across GLP-1 medicines, including dulaglutide, without separating the medicines or showing cause. [6]
Routes from a weekly injection to a cloudy head
- Low blood sugar: with insulin or a sulfonylurea, readings below 54 mg/dL were frequent, for example in about one in five people on a sulfonylurea over 78 weeks. [1] MedlinePlus notes that unclear thinking tends to appear when blood sugar falls further, below 54 mg/dL. [10]
- Tiredness: fatigue, weakness and malaise are grouped together in the US table and were more common than on placebo, rising with dose. [1]
- Fluid loss: nausea, vomiting and diarrhoea are the most frequent reactions, and the label links the resulting dehydration to kidney injury. [1] MedlinePlus lists irritability or confusion and listlessness among the signs of severe dehydration. [9]
- Sleep: insomnia was reported by 1.7% on 1.5 mg against 1.2% on placebo in Canadian data. [4] Cleveland Clinic and MedlinePlus both name lack of sleep as a cause of foggy or confused thinking. [7][8]
- Eating less: decreased appetite rose from 1.6% on placebo to 4.9% and 8.6% on the two original doses. [1] Cleveland Clinic counts healthy meals among the steps that help with brain fog. [8]
Other common causes
Cleveland Clinic describes brain fog as a group of symptoms affecting thinking, memory and concentration that is usually temporary, and lists lack of sleep, diabetes and low blood sugar, hormonal changes such as menopause, stress and long COVID among common causes. [8] MedlinePlus adds fever, infections, alcohol, medicines, fluid and electrolyte imbalance, low oxygen and deficiencies of vitamins such as B12, thiamine or niacin. [7]
MedlinePlus also notes that confusion is more common in older people and can arrive quickly or slowly. [7] In REWIND, more than half of the people on Trulicity® were 65 or older, so these other causes are common in the population that uses it. [1]
What the guidance describes
If you use insulin or a sulfonylurea, the label asks you to learn the signs of low blood sugar and how to treat it, and the EU leaflet advises avoiding driving if any sign appears. [1][3] For sudden confusion from low blood sugar caused by a diabetes medicine, MedlinePlus describes giving a sweet drink or snack and contacting a provider if confusion lasts longer than 10 minutes. [7]
The Medication Guide asks you to drink fluids to lower the chance of dehydration. [2] Cleveland Clinic suggests better sleep habits and healthy meals, and seeing a provider when fog disrupts daily life, for example missed appointments or trouble following conversations. [8]
Trulicity® is a registered trademark of Eli Lilly and Company. PepLabo is not affiliated with or endorsed by Eli Lilly and Company.
When to get help
| Sign | Who to contact | How fast | Source |
|---|---|---|---|
| Confusion that comes on suddenly, especially in someone with diabetes, or with fever, a fast pulse, cold clammy skin or feeling faint | Emergency services (911 / 112) | Emergency | MedlinePlus [7] |
| Confusion, shakiness or sweating while using insulin or a sulfonylurea | Sweet drink or snack as instructed; contact a provider if it lasts more than 10 minutes | Emergency | Medication Guide [2]; MedlinePlus [7] |
| Foggy and listless with vomiting or diarrhoea and very little urine | Your prescriber | Today | Medication Guide [2]; MedlinePlus [9] |
| Ongoing fog that disrupts work, appointments or conversations | Your doctor | At your next appointment | Cleveland Clinic [8] |
