Short answer: In the label's 52-week safety trial of 3,070 people, the most common Cycloset side effects were nausea (32.2% vs 7.6% on placebo), dizziness (14.8% vs 9.2%), fatigue (13.9% vs 6.7%), headache (11.4% vs 8.3%) and vomiting (8.1% vs 3.1%). They lasted a median of 14 days and were more likely during the first dose increases. Cycloset has no boxed warning; low blood pressure and fainting are its first listed risk.
What Cycloset is approved for: Cycloset is an ergot derivative, a dopamine receptor agonist, approved along with diet and exercise to improve blood sugar control in adults with type 2 diabetes (section 1). It should not be used for type 1 diabetes or diabetic ketoacidosis. Efficacy data with thiazolidinediones are limited, and efficacy with insulin has not been confirmed.
Source
CYCLOSET (bromocriptine mesylate) tablets, for oral use, prescribing information and Patient Information. VeroScience (distributed by Avvisto Therapeutics). DailyMed, version published January 14, 2026. DailyMed setid e42ba916-16b9-4d1c-8d09-9d2fbb1b6c20
No. The current Cycloset label has no boxed warning.
These are the label's own numbers from the Adverse Reactions section. Where the label compares with placebo (a dummy treatment), both columns are shown, so you can see how much more often a reaction happened on Cycloset.
| Trial and adverse reaction | CYCLOSET 1.6 mg to 4.8 mg, N (%) | Placebo, N (%) |
|---|---|---|
| Monotherapy, N = 80 vs 79: Nausea | 26 (32.5) | 6 (7.6) |
| Monotherapy: Rhinitis | 11 (13.8) | 3 (3.8) |
| Monotherapy: Headache | 10 (12.5) | 7 (8.9) |
| Monotherapy: Asthenia | 10 (12.5) | 5 (6.3) |
| Monotherapy: Dizziness | 10 (12.5) | 6 (7.6) |
| Monotherapy: Constipation | 9 (11.3) | 3 (3.8) |
| Monotherapy: Sinusitis | 8 (10.0) | 2 (2.5) |
| Monotherapy: Diarrhea | 7 (8.8) | 4 (5.1) |
| Monotherapy: Amblyopia | 6 (7.5) | 1 (1.3) |
| Monotherapy: Dyspepsia | 6 (7.5) | 2 (2.5) |
| Monotherapy: Vomiting | 5 (6.3) | 1 (1.3) |
| Monotherapy: Infection | 5 (6.3) | 4 (5.1) |
| Monotherapy: Anorexia | 4 (5.0) | 1 (1.3) |
| Adjunct to sulfonylurea (2 pooled 24-week studies), N = 244 vs 250: Nausea | 62 (25.4) | 12 (4.8) |
| Adjunct to sulfonylurea: Asthenia | 46 (18.9) | 20 (8.0) |
| Adjunct to sulfonylurea: Headache | 41 (16.8) | 40 (16.0) |
| Adjunct to sulfonylurea: Flu syndrome | 23 (9.4) | 19 (7.6) |
| Adjunct to sulfonylurea: Constipation | 24 (9.8) | 11 (4.4) |
| Adjunct to sulfonylurea: Cold | 20 (8.2) | 20 (8.0) |
| Adjunct to sulfonylurea: Dizziness | 29 (11.9) | 14 (5.6) |
| Adjunct to sulfonylurea: Rhinitis | 26 (10.7) | 12 (4.8) |
| Adjunct to sulfonylurea: Sinusitis | 18 (7.4) | 16 (6.4) |
| Adjunct to sulfonylurea: Somnolence | 16 (6.6) | 5 (2.0) |
| Adjunct to sulfonylurea: Vomiting | 13 (5.3) | 8 (3.2) |
| Adjunct to sulfonylurea: Amblyopia | 13 (5.3) | 6 (2.4) |
| 52-week safety trial, N = 2054 vs 1016: Nausea | 661 (32.2) | 77 (7.6) |
| 52-week safety trial: Dizziness | 303 (14.8) | 93 (9.2) |
| 52-week safety trial: Fatigue | 285 (13.9) | 68 (6.7) |
| 52-week safety trial: Headache | 235 (11.4) | 84 (8.3) |
| 52-week safety trial: Vomiting | 167 (8.1) | 32 (3.1) |
| 52-week safety trial: Diarrhea | 167 (8.1) | 81 (8.0) |
| 52-week safety trial: Constipation | 119 (5.8) | 52 (5.1) |
N (%), all randomized people who took at least one dose. Cycloset was titrated to 1.6 mg to 4.8 mg a day as tolerated. Asthenia means weakness; amblyopia here means blurred or reduced vision.
Low blood sugar: in the monotherapy trial, 2 people on Cycloset (3.7%) and 1 on placebo (1.3%); added to a sulfonylurea, 8.6% vs 5.2%; in the 52-week trial, 6.9% vs 5.3%, with severe low blood sugar in 0.5% vs 1%.
Fainting across clinical trials: 1.4% of 2,500 people on Cycloset vs 0.6% of 1,454 on placebo. In the 52-week trial: 33 people (1.6%) vs 7 (0.7%).
In the 52-week trial, low blood pressure was reported in 2.2% on Cycloset vs 0.8% on placebo. Of those on Cycloset with symptoms, 98% were on at least one blood pressure medicine.
Sleepiness in the 52-week trial: 4.3% on Cycloset vs 1.3% on placebo. None were serious, and most resolved over time.
Serious adverse reactions in the 52-week trial: 176 of 2,054 (8.5%) on Cycloset vs 98 of 1,016 (9.6%) on placebo.
One case of pulmonary fibrosis (0.04% event rate) occurred among 2,500 people on Cycloset in controlled trials.
Reported with other bromocriptine products, generally at higher doses for other conditions: hallucinations and mental confusion, and fibrotic complications such as retroperitoneal fibrosis, pulmonary fibrosis, pleural effusion and pericarditis.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Low blood pressure and fainting. Cycloset can cause low blood pressure on standing and fainting, especially when starting or raising the dose. Standing blood pressure is checked before starting and from time to time after, and caution is used with blood pressure medicines.
Psychotic disorders. Cycloset may worsen severe psychotic disorders or weaken the medicines that treat them. Use in severe psychotic disorders is not recommended.
Impulse control and compulsive behaviors. Intense urges to gamble, spend money, have sex or other urges have been reported with medicines that raise dopamine activity, including bromocriptine. A lower dose or stopping is considered if they develop.
Sleepiness. Cycloset may cause sleepiness. People who feel sleepy are told not to drive or operate heavy machinery.
Dopamine receptor antagonists. Antipsychotic medicines that block dopamine may weaken Cycloset, and Cycloset may weaken them. Using them together is not recommended.
Other dopamine receptor agonists. Safety and effect are unknown in people already taking another dopamine agonist, for example for Parkinson's disease or high prolactin. Using them together is not recommended.
Postpartum use. Cycloset is not used after giving birth. High blood pressure, heart attack, seizures, stroke and psychosis have been reported in postpartum women given bromocriptine to stop milk production.
From the Patient Information and section 17 that comes with Cycloset:
Dose Track has a side-effect log. Each entry records the symptom, a severity (none, mild, moderate, severe or life-threatening), the date and an optional note, and can be tied to a specific dose or logged on its own. The history screen shows what you logged over time, which makes it easier to tell your prescriber when a reaction started and whether it is easing. The app records what you enter; it does not judge whether a symptom is serious. For anything on the label's call-your-doctor list, call your doctor.
This page is what the FDA label says, in plain words. It is not medical advice. Follow your prescriber, and ask them or your pharmacist about anything here.