Short answer: In the 6-month Kyzatrex study of 155 men, the only reaction in 2% or more was hypertension (2.6%, by cuff readings). The study had no placebo group. Hemoglobin rose in 4.5%, headache was reported in 1.9%, and average 24-hour systolic blood pressure rose 1.7 mm Hg at 4 months and 1.8 mm Hg at 6 months. The current label has no boxed warning.
What Kyzatrex is approved for: Kyzatrex is approved as testosterone replacement therapy in adult males with low or absent natural testosterone due to primary hypogonadism (testicular failure) or hypogonadotropic hypogonadism (a pituitary or hypothalamus cause). The label says safety and efficacy have not been established in males under 18 or in men with "age-related" (late-onset) hypogonadism (section 1).
Source
KYZATREX (testosterone undecanoate) capsules, for oral use, prescribing information and Medication Guide. Marius Pharmaceuticals. DailyMed, version published October 8, 2026. DailyMed setid 7f7167a7-2a25-47e2-acf5-33f499fce971
No. The current Kyzatrex 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 Kyzatrex.
| Adverse Reaction | N = 155 n (%) |
|---|---|
| Hypertension* | 4 (2.6) |
155 hypogonadal men in a 6-month study; all started at 200 mg twice daily and were titrated as needed. Mean exposure was 168 days. There was no placebo group. * Based upon blood pressure cuff measurements.
| 24-Hour Ambulatory | Systolic change from baseline (95% CI) mm Hg | Diastolic change from baseline (95% CI) mm Hg |
|---|---|---|
| 4 Month | 1.7 (0.3 to 3.1) | 0.6 (-0.3 to 1.6) |
| 6 Month | 1.8 (0.3 to 3.2) | 0.6 (-0.4 to 1.6) |
24-hour ambulatory blood pressure in Study MRS-TU-2019EXT; 151 men had usable recordings at baseline and follow-up.
In men already on blood pressure medicine, systolic blood pressure rose 3.4 mm Hg at 4 months and 3.1 mm Hg at 6 months. In men without high blood pressure, it rose 0.7 and 1.0 mm Hg. 5 of 155 men (3.2%) started a new blood pressure medicine.
Hemoglobin rose in 7 of 155 men (4.5%); none stopped Kyzatrex because of it. Hematocrit was not measured in this study.
PSA rose more than 1.4 ng/mL from baseline in 4 of 155 men (2.6%), and 2 of 155 (1.3%) had a PSA of at least 4.0 ng/mL. The mean PSA rise was 0.15 ng/mL at 6 months.
One man (0.8%) left the study early because of a side effect (acne). Average 24-hour heart rate rose 0.7 beats per minute at 4 months and 1.9 at 6 months.
In a separate 12-month open-label study (N=212), other reactions reported were headache, joint pain, diarrhea, increased hemoglobin, anxiety, constipation, leg swelling and increased PSA.
The Warnings and Precautions part of the label lists these. Each line gives the label's heading and what it means in plain words.
Polycythemia (high red blood cells). Hematocrit is checked before starting and about every 3 months. If it is high, Kyzatrex is stopped until it falls; if it rises again after restarting, Kyzatrex is stopped for good.
Blood clots. Deep vein thrombosis and pulmonary embolism have been reported with testosterone products. In the TRAVERSE study of a testosterone gel, clots occurred in 1.7% vs 1.2% on placebo. If a clot is suspected, Kyzatrex is stopped.
Enlarged prostate and prostate cancer. Men with an enlarged prostate (BPH) may see their symptoms worsen, and androgens may raise prostate cancer risk. The label says to check for prostate cancer before and during treatment.
Blood pressure increases. Kyzatrex raised average blood pressure by 1.7/0.6 mm Hg after 4 months and 1.8/0.6 mm Hg after 6 months, and by more in men already on blood pressure medicine. Blood pressure is checked periodically, and Kyzatrex is not recommended with uncontrolled high blood pressure.
Abuse and testosterone level checks. Testosterone has been abused at higher-than-approved doses, often with other anabolic steroids, which can cause serious heart and mental health problems. If abuse is suspected, testosterone levels are checked.
Not for use in women. Kyzatrex is not indicated for women because of a lack of controlled studies and possible masculinizing effects.
Sperm production. Large doses of testosterone can suppress sperm production through feedback on the pituitary, which could lower sperm count.
Liver effects. Kyzatrex is not a 17-alpha-alkyl androgen and is not known to cause liver problems, which have been linked to long high-dose use of that type. If signs such as jaundice appear, Kyzatrex is stopped while the cause is checked.
Edema (fluid retention). Androgens can cause the body to hold salt and water. Swelling, with or without heart failure, can be serious in people with heart, kidney or liver disease.
Sleep apnea. Testosterone may worsen sleep apnea, especially with obesity or chronic lung disease.
Gynecomastia. Breast enlargement may develop and persist.
Lipid changes. In trials, total cholesterol, LDL, HDL and triglycerides went down on Kyzatrex. Lipid changes may require a change in cholesterol medicine or stopping testosterone, and lipids are checked periodically.
High calcium. In cancer patients at risk of high calcium, Kyzatrex is used with caution and calcium is checked periodically.
Thyroid lab values. Androgens can lower thyroxine-binding globulin and total T4 on lab tests, but free thyroid hormone stays the same and there is no sign of thyroid disease.
From the Medication Guide that comes with Kyzatrex:
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.