| Marker | Gabriel optimal | Typical lab range | Functional range |
|---|---|---|---|
| Hematocrit Men | 40 to 48 % | 37.5 to 51 | 40 to 48 |
| Hematocrit Women | 37 to 44 % | 34 to 46.6 | 37 to 44 |
Common side effects
- Acne or oily skin
- Mild fluid retention, such as ankle swelling
- Breast enlargement or tenderness
- Smaller testicles and lower sperm count
- Urinary symptoms from prostate stimulation
- Skin irritation with gels and patches; pain or bruising at injection sites
- Lab changes: higher hematocrit and a rising PSA
Serious risks to know
- High hematocrit (erythrocytosis). More red blood cells thicken the blood. The Endocrine Society advises pausing therapy above 54% and not starting if hematocrit is already above 48% (50% at high altitude). See high hematocrit on TRT.
- Blood pressure. In 2025 the FDA required a blood pressure warning on all testosterone products after studies confirmed a class-wide increase.
- Sleep apnea can get worse.
- Prostate. TRT can raise PSA, so it is checked before and during treatment. Men with prostate or breast cancer should not use it.
- Misuse at high doses can cause heart attack, stroke, liver disease and mood changes, and stopping can cause withdrawal symptoms such as depression.
Call your clinician promptly for leg pain or swelling, breathing trouble during sleep, an erection that lasts too long, blood in the urine, yellow skin or eyes, or new depression. Call 911 for chest pain, sudden shortness of breath, or signs of a stroke.
What the heart safety data show
The FDA warned in 2015 about possible heart risk. In February 2025, after the TRAVERSE trial found no increase in major heart events in men using testosterone for hypogonadism, the FDA removed that boxed warning from all testosterone products. Long-term data are still limited, and evidence on blood clots is mixed.
How long TRT takes to work
- A few weeks: it may take this long to notice differences in mood and body.
- About a month: clinicians commonly recheck testosterone around 30 days after starting.
- 3 to 6 months: time to judge whether symptoms improved. If not, testosterone may not be the cause.
TRT and fertility
TRT lowers sperm count, which can cause infertility. Restoring fertility afterward can be slow and costly. The Endocrine Society recommends against TRT for men planning a pregnancy soon. If you might want children, raise it before you start.
Monitoring and your optimal hematocrit
Expect testosterone, hematocrit and PSA checks in the first year, plus blood pressure. The table below shows the typical lab range and the Gabriel optimal range for hematocrit. You can upload any lab report and Gabriel explains it in plain words. Read more in the hematocrit blood test guide.
Common questions
Is TRT safe long term?
With monitoring, many men use it for years, but long-term data are limited. The 2025 FDA update found no rise in major heart events in the TRAVERSE trial, and blood pressure and hematocrit still need watching.
Does TRT cause acne?
It can. Acne and oily skin are among the most common side effects. Tell your clinician if it becomes a problem.
Does TRT make you infertile?
It can. TRT lowers sperm production, and fertility may take a long time to return. Tell your clinician if you want children.
How long does it take for TRT to work?
Many people notice changes within a few weeks. Clinicians usually judge the full effect at 3 to 6 months.
Can TRT raise blood pressure?
Yes. The FDA requires a blood pressure warning on all testosterone products, so your clinician should check it before and during treatment.
Sources
- Testosterone replacement therapy (TRT) Cleveland Clinic
- Testosterone therapy in men with hypogonadism: an Endocrine Society clinical practice guideline Journal of Clinical Endocrinology & Metabolism (Bhasin et al., 2018)
- FDA issues class-wide labeling changes for testosterone products U.S. Food and Drug Administration
- Testosterone injection MedlinePlus, National Library of Medicine
This guide is general information, not medical advice. It does not replace a visit with a licensed clinician. Gabriel membership is not health insurance.